Lissa Percopo is a partner in Gibson, Dunn & Crutcher’s Washington, D.C. office, where she is a member of the Firm’s Litigation Department. Lissa focuses her practice on securities litigation, with an emphasis in securities class actions and shareholder derivative actions. She represents clients at all stages of litigation, from pre-complaint counseling through appeals, and she regularly practices in state and federal courts around the country.
Representative Matters
- Defending HP Inc. and its current and former directors and officers in two securities class actions and related derivative suits in the U.S. District Court for the Northern District of California and the Ninth Circuit. Won consecutive motions to dismiss in one securities class action. The second is on appeal to the Ninth Circuit after the district court denied our motion to dismiss in part but granted our motion for interlocutory appeal on a novel statute of repose issue.
- Defending Energy Transfer LP, the country’s largest pipeline company, as well as its senior officers and directors in both E.D. Pennsylvania and N.D. Texas securities class action and shareholder derivative actions challenging statements regarding various pipeline construction projects. Secured major win on summary judgment in the E.D. Pennsylvania securities class action, leading to favorable settlement. The motion to dismiss the N.D. Texas action remains pending.
- Defending DocGo Inc. in a securities class action and certain directors/officers in derivative litigation related to statements regarding the former CEO’s credentials and company’s business prospects.
- Defending Rentokil Initial plc and certain officers in a securities class action in the W.D. of Tennessee over alleged misrepresentations tied to its $6.7B acquisition of Terminix Inc.
- Defending fitness franchisor F45 in a securities class action in the W.D. of Texas challenging IPO statements about its business model and performance.
- Defending Goldman Sachs, JPMorgan, and Bank of America in securities litigation in the Southern District of New York related to the IPO of LNG exporter Venture Global.
- Defended Bank OZK and its leadership in class and derivative actions in the E.D. of Arkansas following a stock drop tied to commercial loan write-downs. Achieved partial dismissal in the class action, full dismissal of the federal derivative suit, and resolution of remaining claims within policy limits.
- Represented JCPenney and certain officers in a securities class action over liquidity-related disclosures. Secured Fifth Circuit review of class certification and negotiated an insurance-funded settlement.
- Represented Danimer Scientific in a securities class action and Second Circuit appeal challenging statements about the biodegradability of its flagship product.
Lissa has been recognized by the Legal 500 US as a “Recommended Lawyer” in Securities Litigation: Defense for 2025. Lissa is also a seasoned general litigator, having represented clients in a variety of complex litigations, including class action, antitrust, contract dispute, and consumer fraud cases.
She serves on the Firm’s Hiring and Professional Development Committees, and she previously served on the Firm’s Associates’ Committee. She currently serves on the D.C. Office’s Diversity Committee. Lissa joined the firm in 2007 after graduating with highest honors from the George Washington University Law School. While at George Washington, she was a member of the George Washington International Law Review, and was elected to Order of the Coif. Lissa has also been an Adjunct Professor at the George Washington University Law School, where she taught Legal Research & Writing and Introduction to Advocacy.
Lissa graduated from the University of Virginia in 2001, with a Bachelor of Arts degree in History. She is a member of the bars of New York and the District of Columbia.
Mark Goldman is of counsel in the Los Angeles office of Gibson Dunn. He is a member of the firm’s Emerging Companies / Venture Capital, Mergers and Acquisitions and Private Equity Practice Groups. He represents investment funds and companies in connection with venture capital, growth equity, and control investments. His experience also includes merger transactions, stock and asset sales, and joint ventures across a wide range of industries.
Prior to joining Gibson Dunn, Mark was a corporate lawyer in Israel and before that in Sydney, Australia.
His recent experience in VC and growth transactions includes advising:
- Acumen Fund in its investments in BioMassters, Inclusively, Keep It Cool, Kurasa and Winock Solar
- Blue Earth Capital in its investments in AMP Robotics, CarbonCure, Sense Labs, SWTCH and TS Conductor
- J.P. Morgan’s growth equity arm in its investments in AlphaSense and Loop, among others
- KKR in its investments in Replay and Guesty, among others
- March Capital in its investments in Acceldata, ActionIQ, Expel, Extend, Forter, Gr4vy, Luminance, Nile Global, Overjet, Parallel Domain, SuperOps, Tessera Therapeutics, Tessian, ThoughtSpot and Uniphore, among others
- The Chernin Group in its investment in Lovevery
In addition, his recent experience in M&A transactions includes advising:
- Owners of a SaaS business focused on regulatory reporting solutions in its sale to a strategic buyer
- Platinum Equity in its acquisition of Mad Engine
- KKR and its portfolio company Reliaquest in its acquisition of Digital Shadows
- The Chernin Group in its acquisition of a majority stake in SketchyMedical
- Owners of a platform of dental implant practices in sale of the platform to a private equity group
- Family-owned plush toy business in its sale to a private equity group
Mark is a contributor to Gibson Dunn’s Biotech Briefings blog. View his articles here.
Mark received an M.A. in Government from the Interdisciplinary Center Herzliya (Israel) in 2010. He received an LL.B. and B.Com. from the University of Western Australia in 2005.
Isabel Berger is a partner in the London office of Gibson Dunn. Isabel is a member of the Private Equity, Mergers and Acquisitions, and Real Estate Practice Groups.
Isabel advises private equity funds and other financial investor clients on domestic and cross-border transactions including leveraged buyouts, acquisitions and divestitures, equity growth investments, joint ventures, and co-investments and management equity plans, as well as related advisory work. She has experience advising sponsors across a broad range of industries including real estate private equity transactions. She has previously spent 12 months on secondment at KKR.
Isabel is recognised by Legal 500 UK 2023, 2024 and 2025 for Private Equity: Transactions – high-value deals and Real Estate: Commercial Property – Investment, by Legal 500 UK 2025 for Venture Capital and by Expert Guides as a Rising Star in their 2022 Guide, which recognizes the brightest and most talented practitioners under 40 in the area of business law and related practices. Isabel has been named by The Hedge Fund Journal to its 2025 list of 50 Women Leaders in Private Markets and a Private Equity Rising Star for 2023 by Law.com International: one of the top 25 private equity lawyers under 40 in the U.K. and Europe.
Isabel is admitted to practice in England and Wales and is fluent in English and German.
Selected experience:*
- H.I.G. Capital on various transactions, including:
- the acquisition of TIMETOACT, a software consulting business.
- the acquisition of Spheros group, Valeo’s former bus thermal solutions business.
- Mubadala Capital in connection with the hybrid preferred equity financing for its take-private of CI Financial Corp.
- KKR on various transactions, including:
- its growth investment in Premialab, an independent data and risk analytics platform used by institutional investors looking to monitor, manage, and diversify their global portfolios.
- its growth investment in Lighthouse, a leading data analytics and commercial intelligence platform for the travel and hospitality industry.
- its majority acquisition of Biosynth Carbosynth, a life sciences reagents and custom synthesis and manufacturing services compan y.
- its investment in Leapwork, a Danish no-code automation platform.
- its investment in Feedzai, a cloud-based financial risk management platform.
- its investment and follow-on investment in music platform Artlist.
- its investment in low code platform, Outsystems.
- Dawn Bio on various transactions, including:
- its investment in Adcendo.
- its investment in Antag Therapeutics.
- its inve stment in Adcytherix.
- its investment in Agomab.
- its investment in Bambusa Therapeutics.
- its investment in Expedition Therapeutics.
- TowerBrook Capital Partners on various transactions, including:
- its investment in Aernnova, a Spanish company specialising in the design and manufacturing of aerostructures and component parts.
- its acquisition of Van Dijk Educatie, a Dutch provider of learning materials.
- Mid Europa Partners on its sale of Alpha Medical to Unilabs, an Apax Partners portfolio company.
- KKR Real Estate on various transactions, including:
- its equity arrangements with European hospitality partner Amante Capital.
- its equity arrangements with European logistics partner Mirastar.
- its equity arrangements with living specialist partner inhabeo.
- its majority investment in Fore’s Tower Bridge office scheme, a 110,000 sq ft development next to Tower Bridge.
- its joint venture with Apache Capital Partners to create a U.K. build-to-rent multi-family housing investment platform.
- its joint venture with Moda Living to create a U.K. build-to-rent investment platform.
- its acquisition of the Heal’s building.
- its joint venture with Relentless to develop a mixed-use scheme in Manchester.
- its acquisition of Velero, a German asset manager specialised in residential properties.
- Sixth Street Partners on the formation of a real estate development finance platform with Maslow Capital.
- Roundshield Partners on the formation of a real estate development finance platform with Puma Property Finance.
- Asterion Industrial Partners on equity arrangements relating to its acquisition of data centers from Telefónica.
- Buckthorn Partners in connection with its investment in TWMA Group Limited.
- Inspired Entertainment, Inc., a leading supplier of gaming terminals in the UK, on the acquisition of the Gaming Technology Group of Novomatic UK Ltd.
- Crayhill Capital Management on:
- its financing of Heroes, a UK-based technology driven ecommerce company.
- its financing for unybrands, an integrated platform for e-commerce businesses.
*Some of these representations occurred prior to Isabel’s association with Gibson Dunn.
George Venables is an Of Counsel in the London office of Gibson Dunn and is a member of the Mergers and Acquisitions, Energy and Infrastructure and Oil and Gas Practice Groups.
George has a broad corporate practice advising on the full spectrum of commercial transactions, with a focus on the energy and infrastructure sectors, including relating to upstream, midstream and downstream oil and gas, power, energy infrastructure and renewables and energy transition infrastructure. He has extensive experience advising a range of clients on the full spectrum of mergers and acquisitions, disposals, restructurings, project development, and joint ventures both in the UK and internationally.
Prior to joining Gibson Dunn, George worked in the London office of another major global law firm.
Selected experience*:
- TotalEnergies on the merger of its UKCS upstream business with NEO NEXT to become the leading shareholder (47.5%) in the expanded NEO NEXT+ joint venture, alongside HitecVision (28.875%) and Repsol (23.625%), forming the largest independent oil and gas producer in the UKCS
- MidOcean Energy, an LNG company formed and managed by EIG Global Energy Partners, on its acquisition of a 20% interest in PETRONAS’ interest in the LNG Canada Project, by way of acquisition of a 20% interest in the North Montney Upstream Joint Venture and a 20% interest in the North Montney LNG Limited Partnership, and the entry into associated joint venture arrangements to govern such investment
- EIG Global Energy Partners on its acquisition of a 25% equity interest stake in Repsol Upstream, a newly formed global oil and gas exploration and production company holdings Repsol’s global upstream oil and gas portfolio, for US$4.8 billion, and the associated joint venture arrangements
- Chevron on the disposal of its UK North Sea upstream business to Ithaca Energy for US$1.6billion
- ExxonMobil on the sale of material Nigerian oil and gas assets to Seplat Energy
- ExxonMobil on the disposal of upstream and midstream assets in Chad and Cameroon, including its interest in the Chad-Cameroon pipeline, to Savannah Energy plc
- Navitas Petroleum on the acquisition of a 65% stake in the Sea Lion project, an oil field located offshore of the Falkland Islands, via the acquisition of Premier Oil Exploration and Production from Harbour Energy and participating interests from Rockhopper Exploration
- SierraCol Energy (a portfolio company of the Carlyle Group) on its US$825 million acquisition of Occidental Petroleum’s entire onshore oil and gas portfolio in Colombia
- The Carlyle Group on the proposed acquisition of a portfolio of gas-weighted exploration and production assets in Italy, Egypt, and Croatia from Energean
- RWE on its acquisition of the Norfolk Vanguard offshore wind portfolio from Vattenfall
- RWE on the sale of a 49% equity interest in the Dogger Bank South wind farm project to Masdar, and entry into the associated joint venture arrangements
- GIC on its investment, alongside Partners Group, TPG Rise Climate and Mubadala, into Techem, an international provider of digitally enabled solutions for the real estate sector, at an enterprise value of around EUR 6.7 billion
- KKR on its £3.4billion acquisition of Encavis, a German headquartered independent power producer with solar parks and onshore wind farms in 12 European countries
- ADNOC and OMV on acquiring Nova Chemicals from Mubadala for $13.4 billion
- GIC on acquiring an approximately 45% shareholding in GasLog, an international owner, operator, and manager of LNG carriers, from BlackRock
- Chevron on the US$900 million sale of its refinery and fuels network in South Africa and Botswana to Sinopec
* Some of these representations occurred prior to George’s association with Gibson Dunn.
Melissa W. Kopit is of counsel in the Washington, D.C. office of Gibson, Dunn & Crutcher. She is a member of the Finance and the Transportation and Space Practice Groups.
Melissa advises lenders, underwriters, borrowers, lessors, lessees, equity participants and other financiers in a wide range of cross-border and domestic transactions. Her practice focuses on asset finance and leasing transactions for commercial and business aircraft, helicopters and general equipment assets.
Melissa was recognized in The Best Lawyers in America® Ones to Watch for her work in Banking and Finance Law and Transportation Law in 2024 and 2025. She was also named as a Washington D.C. Rising Star by Super Lawyers from 2022-2024.
She is the 2024 President and a board member of the Washington, D.C. Chapter of the Coalition of Women’s Initiatives in Law.
Melissa received her law degree from George Washington University Law School in 2014, and a Bachelor of Arts degree in International Studies and Political Science in 2009 from the University of North Carolina at Chapel Hill. Prior to joining Gibson Dunn, Melissa was a member of the Global Transportation Finance team at Vedder Price P.C.
Connor Mui is a litigation associate in the Washington, D.C. office of Gibson Dunn. He practices in the firm’s Appellate & Constitutional Law, First Amendment & Free Expression, and Administrative Law & Regulatory Practice Groups. He has significant experience with constitutional, statutory, and APA challenges to government action and has represented multiple organizations with First Amendment claims against the federal or state governments.
Connor served as a law clerk to Justice Amy Coney Barrett of the Supreme Court of the United States, Judge J. Harvie Wilkinson III of the U.S. Court of Appeals for the Fourth Circuit, and Judge Kevin C. Newsom of the U.S. Court of Appeals for the Eleventh Circuit.
Connor earned his J.D. from Yale Law School, where he was a Forum editor for the Yale Law Journal, an executive editor and articles editor for the Yale Journal on Regulation, and a member of the Supreme Court Clinic.
Before law school, Connor spent three years as a management consultant with McKinsey & Company serving public and private sector clients. He also received an M.Phil in philosophy from the University of Cambridge. Connor earned his undergraduate degree in philosophy and public affairs, summa cum laude and Phi Beta Kappa, from Princeton University.
Connor is a member of the bars of New York and the District of Columbia. He is admitted to practice in the U.S. Courts of Appeals for the Second, Fourth, Fifth, Eighth, Tenth, and Eleventh Circuits, the U.S. District Court for the District of Columbia, and the U.S. Court of International Trade.
Trevor Owens is of counsel in the Los Angeles office of Gibson, Dunn & Crutcher, where he practices in the firm’s Real Estate Department.
Trevor specializes in the representation of foreign and domestic banks, insurance companies, debt fund managers, REITs, private equity firms and other institutional lenders in all aspects of complex real estate finance transactions, including the origination of mortgage and mezzanine loans secured by commercial properties comprising all types and sizes of asset classes; the syndication, purchase and sale of whole loans and notes, together with the related intercreditor and/or co-lender agreement negotiations; equity investments through preferred equity arrangements; and restructurings, workouts and deeds-in-lieu of foreclosure.
Trevor earned his law degree in 2009 from the UCLA School of Law, with a Business Law & Policy specialization, and where he was a member of the UCLA Business Law Association and the UCLA Journal of International Law and Foreign Affairs. He received his Bachelor of Arts from the University of California, Santa Barbara in 2004.
Prior to joining the firm, Trevor was an associate in the real estate department of two other international law firms.
Trevor is a member of the California, New York, and Texas Bars.
Select representative transactions include:
- Represented a debt fund manager in connection with its origination of $190M in mortgage and mezzanine loans to finance the ground up construction of a nationally branded hotel, including addressing issues related to C-PACE financing, opportunity zone investments, and municipal bond financings
- Represented a bank in connection with its origination of a $800M mortgage loan to finance the acquisition of a national portfolio of properties of different asset classes, including subsequent note syndications
- Represented a debt fund manager in connection with its origination of $80M in mortgage and mezzanine loans to finance the conversion on a historic industrial building into a mixed-use hotel and event space in New York City, including addressing issues related to historic tax credits and municipal ground leases
- Represented a debt fund manager in connection with its origination of a $184M mortgage loan and $46M preferred equity investment to finance the acquisition and renovation of a portfolio of office properties in Northern California
- Represented a REIT in connection with its purchase of a $53M mezzanine loan secured by the equity interests in the owner of a major hotel and resort in Florida
- Represented an insurance company in connection with its origination of a $470M mortgage loan to finance the acquisition of a national portfolio of industrial properties
Sarah Lefsky is a senior associate in the New York office of Gibson Dunn. She is a member of the firm’s Finance Practice Group.
Sarah represents asset managers and lenders in a range of financing transactions involving investment funds, including private equity, private credit, secondaries and real estate funds. She maintains a broad and sophisticated practice, with experience in subscription-based, NAV-based and hybrid facilities, rated note feeder and collateralized fund obligation transactions and other bespoke secured and structured financings.
Prior to joining Gibson Dunn, Sarah was an associate at another leading international law firm as a member of the Finance practice group.
Sarah earned her Juris Doctor cum laude from New York University School of Law in 2018 and a Bachelor of Arts degree in Government from Cornell University in 2011.
Sarah is admitted to practice in the State of New York.
Loni is an associate in the San Francisco office of Gibson Dunn and a member of the firm’s Real Estate Practice Group. Her practice encompasses a wide range of commercial real estate transactions, including complex leasing, development, construction, acquisitions, dispositions, and joint ventures across numerous asset classes, including mixed-use projects, shopping centers, multifamily, industrial, research and development facilities, medical office, hotels and resorts, and office buildings. She represents owners, institutional landlords, tenants, developers, lenders, investors, and operators across a variety of industries, including retail, technology, hospitality, and energy.
Loni has been recognized by Best Lawyers: Ones to Watch® in America in Real Estate Law (2026).
Loni received her Juris Doctor from Loyola Law School, where she served as an editor of the Loyola of Los Angeles Entertainment Law Review. She earned her Bachelor of Arts in History from the University of Florida. Prior to attending law school, Loni worked for several private and publicly traded REITs.
Loni is admitted to practice law in the State of California.
Lettie Rose is an associate in the New York office of Gibson Dunn where she practices in the firm’s Finance Practice Group.
Lettie specializes in financings for private equity, debt, and other investment funds, including asset-based facilities, subscription-based facilities, and hybrid facilities. Clients also benefit from Lettie’s experience in rated note feeder and collateralized fund obligation transactions.
Lettie received her Juris Doctor from Georgetown University Law Center, where she served as an Annual Review Executive Editor on the Georgetown Journal of Gender and the Law. She graduated from the University of Virginia with a Bachelor of Arts degree in American Government and Politics.
Lettie is admitted to practice in the State of New York.
Alice Yiqian Wang is an associate in the Washington, D.C. office of Gibson Dunn. She practices in the firm’s Litigation Department.
Alice earned her law degree from Yale Law School. She also holds a Ph.D. in Political Science from Stanford University, where her research focused on causal inference, presidential power, and immigration policy. Previously, she received a master’s degree in Political and Legal Theory from the University of Warwick, which she attended on a U.S.-U.K. Fulbright Scholarship. She graduated with degrees in Government and Philosophy from Smith College.
Alice is admitted to practice law in the District of Columbia.
Joshua S. Lipshutz serves as Partner & Chief Operating Officer of Gibson Dunn. He practices in the firm’s Litigation Department, and the Appellate and Constitutional Law, Privacy and Cybersecurity, and Class Actions Practice Groups. Josh is a member of the firm’s Executive and Management Committees.
Josh’s practice focuses primarily on constitutional, class action, data privacy, and securities-related matters. He has been profiled by Law360 for his exceptional appellate experience (Appellate Practice Group of the Year), recognized as a Cybersecurity and Data Privacy MVP in 2019, and recognized as a Technology MVP in 2023. The National Law Journal profiled Josh in both the General Litigation and Labor & Employment categories. Benchmark Litigation has consistently recognized Josh on its Top 50 Labor & Employment Litigators list, and named him both a Labor and Employment Star and a Litigation Star. The Legal 500 United States has recognized him as a “Leading Lawyer” for Labor and Employment Disputes.
Prior to attending law school, Josh received his undergraduate degrees, summa cum laude, in finance and systems engineering, from The Wharton School of the University of Pennsylvania. He graduated Order of the Coif from Stanford Law School, where he was Senior Articles Editor of the Stanford Law Review. Josh served as a judicial clerk to the Honorable Antonin Scalia of the Supreme Court of the United States and the Honorable Alex Kozinski of the United States Court of Appeals for the Ninth Circuit. Before practicing law, Josh worked as a principal investment professional at Silver Lake Partners and as an investment banking associate at Goldman, Sachs & Co.
Josh is admitted to practice law in the State of California, the District of Columbia, and the Commonwealth of Massachusetts.
Chris Whittaker is a partner in the Orange County office of Gibson Dunn. He is a member of the firm’s Litigation Department and its Antitrust and Competition, Intellectual Property, and Labor and Employment Practice Groups. Chris represents clients in a wide range of high-stakes, complex commercial cases, and he has significant experience in a broad range of subject areas, including pharmaceuticals, software development and maintenance, oil and gas, app store and handheld phone technology, semiconductors, logistics operations, health and beauty products, and direct-sales business models. Chris is experienced in all phases of litigation, including pleadings, discovery, dispositive motions, trials, and appeals. He currently serves on the national leadership team of the Federal Bar Association’s Antitrust and Trade Regulation Section.
Chris has been recognized by Best Lawyers: Ones to Watch® in America for Appellate Practice, and Litigation – Intellectual Property (2024).
Prior to joining the firm, Chris served as a law clerk to the Honorable Ted Stewart, then-chief judge of the U.S. District Court for the District of Utah, and the Honorable J. Clifford Wallace of the U.S. Court of Appeals for the Ninth Circuit.
His representative matters include:
- Defending Chevron U.S.A. Inc. in a federal price-fixing class action against direct and indirect purchasers. The Court granted summary judgment on all claims and entered final judgment for all defendants.
- Defending major technology company against monopolization and patent infringement claims brought by an app developer in the District of Delaware. The Court dismissed all claims with prejudice and the Federal Circuit issued a summary affirmance.
- Defending a software company in MDL litigation alleging algorithmic price-fixing among lessors of multifamily and student housing.
- Defending Merck & Co., Inc in litigation where plaintiffs allege an unlawful agreement and conspiracy to delay generic competition
- Defending software support company Rimini Street Inc. in federal suits involving copyright infringement, competition, and business tort claims.
- Defending Amazon in multiple wage and hour class actions in California state and federal court.
- Defending Melaleuca, Inc. in an independent contractor misclassification class action in federal court. The district court compelled the named plaintiffs’ claims to arbitration and the Ninth Circuit affirmed.
Chris received his law degree magna cum laude from Brigham Young University in 2011, where he was elected to the Order of the Coif and served as an editor for the BYU Law Review. In 2007, Chris earned a Bachelor of Arts degree magna cum laude from Brigham Young University-Hawaii.
Connie Lee is an associate in the Washington, D.C. office of Gibson Dunn. She practices in the Litigation Department with a focus on antitrust and competition, where she represents clients in high-stakes litigation matters, including at the trial stage.
Representative matters include:
- Member of the trial team representing Community Health Systems in FTC v. Novant Health (W.D.N.C.), which defeated the FTC’s motion for a preliminary injunction.
- Represented the claimant, a financial services company, in an antitrust arbitration alleging conduct claims.
- Representing a medical equipment manufacturer in a competitor lawsuit alleging monopolization claims.
- Representing a pharmacy benefit manager in a proceeding before the FTC.
Connie also maintains an active pro bono practice and served as the lead attorney in winning a grant of asylum for a client in an immigration court hearing in 2022.
She received her Juris Doctor from Columbia Law School, where she was a Harlan Fiske Stone Scholar and served as a Note Editor on the Columbia Human Rights Law Review. She received her Bachelor of Arts degree from Dartmouth College in Government and Philosophy. During law school, Connie served as a judicial extern to the Honorable Raymond J. Lohier of the United States Court of Appeals for the Second Circuit.
Connie is admitted to practice law in the District of Columbia.
Helgi Walker is a partner in Gibson Dunn’s Washington, D.C. office. She is Co-Chair of the firm’s global Litigation Practice Group and recently served as a member of the firm’s Executive Committee. She is also Co-Chair of the Administrative Law and Regulatory Practice Group and a member of the Appellate and Constitutional Law Practice Group. Chambers USA describes her as “dynamite in the courtroom and a forceful oral advocate,” “a brilliant legal mind,” and counsel with “excellent judgment” and “a reputation for excellence.”
Helgi’s work focuses on appellate, regulatory, and complex litigation matters. She has extensive experience in appellate challenges to agency rulemakings and in other high-stakes commercial litigation.
Helgi was elected as a Fellow of the American Academy of Appellate Lawyers, limited to 500 lawyers nationwide. She also is a member of the U.S. Chamber of Commerce’s Administrative Law & Government Litigation Advisory Committee. By appointment of the U.S. Court of Appeals for the D.C. Circuit, Helgi served as the Chair of the Court’s Advisory Committee on Procedures from 2017-2024. From 2010 to 2015, she was a Public Member of the Council of the Administrative Conference of the United States, composed of leading authorities on administrative law.
Helgi worked in the White House Counsel’s Office as Associate Counsel to President George W. Bush from 2001 to 2003.
Helgi clerked for U.S. Supreme Court Justice Clarence Thomas from 1995 to 1996 and Judge J. Harvie Wilkinson III of the U.S. Court of Appeals for the Fourth Circuit from 1994 to 1995.
Helgi is listed as a leading lawyer in Appellate Law Telecom, Broadcast & Satellite and Commercial Litigation by Chambers USA. In its 2020 competition, The American Lawyer named Gibson Dunn the Litigation Department of the Year and a finalist in the White Collar/Regulatory category that includes her practice areas. In 2011, The American Lawyer selected her as one of the “45 Under 45,” “best of the best among young women lawyers” in the United States. The National Law Journal named her one of “Washington’s Most Influential Women Lawyers” in 2011. Washingtonian magazine has repeatedly recognized her as one of D.C.’s “Top Lawyers” in its biennial rankings, including in the Supreme Court (2022) and Communications (2024) categories, and among “The Power 100” of “influential players running Washington and the world” (2014-2015).
In addition, she was :
- Named The American Lawyer’s “Litigator of the Week” for securing a ruling blocking the FTC’s “Click to Cancel” rule (2025).
- Named The American Lawyer’s “Litigator of the Week” runner-up for securing a writ of mandamus from the Fifth Circuit ordering the FTC to comply with the federal lottery statute (2024).
- Named The American Lawyer’s “Litigator of the Week” runner-up for successful challenge to the SEC’s dealer rule (2024).
- Named by Benchmark Litigation as a “Litigation Star” (2026).
- Named by Benchmark Litigation as a “National Practice Area Star” in Appellate (2026).
- Named one of Benchmark Litigation’s “Top 250 Women in Litigation” in the country (2021-2025).
- Named by Lawdragon as one of the “500 Leading Litigators in America” (2024-2026).
- Named by Lawdragon as a “Lawdragon Legend” (2021), one of only 32 lawyers nationwide recognized as “the biggest stars” who have demonstrated “sustained excellence and endurance.”
- Named by Client Choice Awards as the winner of the District of Columbia Litigation category (2018).
- Named by Law360 as a Telecommunications MVP (2016), observing that her work “has spanned the industry” including a “big win” for broadcasters in “a major ownership case.”
- Named by Law360 as an Appellate MVP (2015), describing her as a “go-to counsel for high-stakes appellate challenges of federal agency actions” and “leading cutting-edge litigation for a range of industries.”
- Named The American Lawyer’s “Litigator of the Week” for her win on behalf of Ford Motor Company before the en banc Sixth Circuit in a case involving telecommuting under the Americans with Disabilities Act (2015).
- Named The American Lawyer’s “Litigator of the Week” for her win on behalf of Verizon in the “major appeals court ruling” overturning the FCC’s “net neutrality” regulation of Internet service providers (2014).
- Named The American Lawyer’s “Litigator of the Week” for obtaining a “blockbuster appellate decision” for Comcast in a challenge to the FCC’s first “net neutrality” decision (2010).
Representative Matters:
- Represented the Dewberry Group in U.S. Supreme Court in 9-0 victory in appeal regarding trademark remedies.
- Represented the National Association of Broadcasters and other media and newspaper industry parties as lead counsel in the U.S. Supreme Court in defense of the FCC’s repeal or modification of restrictive and outdated local media ownership rules, arguing the case and winning 9-0.
- Represented the Interactive Advertising Bureau, NCTA, the U.S. Chamber of Commerce, NFIB, and others comprising a broad coalition of trade associations and businesses challenging the FTC’s “click to cancel” rule, obtaining vacatur of the entire rule in the Eighth Circuit just days before it was set to take effect, as well a prior mandamus order from the Fifth Circuit directing the agency to comply with the federal lottery statute governing multi-circuit petitions for review.
- Represented the National Association of Broadcasters in latest challenge to FCC media ownership rules in the Eighth Circuit, securing vacatur of rule prohibiting broadcasters from owning more than one top-four-rated television station and establishing precedent that the Telecommunications Act of 1996 does not allow tightening of the rules only deregulation.
- Represented the National Association of Private Fund Managers, and other private funds trade associations, in winning Fifth Circuit challenge to SEC rule asserting proscriptive authority over private funds, securing vacatur of the entire rule.
- Represented the National Association of Private Fund Managers, and other private funds trade associations, in successful N.D. Texas challenge to SEC’s “dealer” rule, resulting in vacatur of entire rule.
- Representing T-Mobile in D.C. Circuit appeal of FCC enforcement action imposing $80 million penalty regarding location data.
- Represented CTIA-The Wireless Association in the D.C. Circuit in successfully upholding the FCC’s “Restoring Internet Freedom Order” repealing the “net neutrality” regime and most recently in overturning the subsequent reinstatement of those rules in the Sixth Circuit.
- Represented Verizon in successful D.C. Circuit appeal of the FCC’s order formally adopting “net neutrality” rules, obtaining vacatur of the rules.
- Represented Comcast in successful D.C. Circuit appeal of the FCC’s first “net neutrality” decision, securing vacatur of that decision.*
- Represented PHH Corporation in D.C. Circuit appeal of CFPB action under the Real Estate Settlement Procedures Act of 1974—the first appellate challenge to a CFPB enforcement proceeding—and successfully procured a stay of the agency order pending appeal and victory on the merits in a historic separation of powers ruling at the panel level, ultimately prevailing before the en banc court on administrative law grounds and securing vacatur of $109 million penalty.
- Appointed by the U.S. Supreme Court to brief and argue the case in defense of the judgment below in Welch v. United States, involving the retroactivity of new rules on habeas review.
* Matter handled prior to joining Gibson, Dunn & Crutcher LLP.
Helgi graduated in 1994 from the University of Virginia School of Law, where she was a member of the Order of the Coif and Raven Society and served as Executive Editor of the Virginia Law Review. She also received the Robert E. Goldsten Award and John M. Olin Prize in Law and Economics.
Helgi is admitted to practice in the District of Columbia.
Jeff Liu is an associate in the Washington, D.C., office of Gibson Dunn. He practices in the firm’s Litigation Department.
Before joining the firm, Jeff served as an attorney-adviser in the Department of Justice’s Office of Legal Counsel, where he prepared legal advice for the President and executive branch agencies on a range of statutory and constitutional questions. He was previously a law clerk to the Honorable Carlos T. Bea of the U.S. Court of Appeals for the Ninth Circuit.
Jeff earned his J.D. from Stanford Law School, where he served as an Articles Editor on the Stanford Law Review and earned the Judge Thelton E. Henderson Prize for his contributions in the Stanford Supreme Court Litigation Clinic. He graduated summa cum laude with a dual degree in Chemical Engineering and Philosophy from Auburn University.
He is admitted to practice law in California and the District of Columbia. Jeff is also admitted to practice before the U.S. Court of Appeals for the Ninth Circuit.
Kristen Limarzi is a partner in the Washington, D.C. office of Gibson Dunn and Global Co-Chair of the firm’s Antitrust and Competition Practice Group. Prior to joining the firm, she served as a top enforcement official in the U.S. Department of Justice’s Antitrust Division, where, as Section Chief, she helped shape and implement the agency’s enforcement priorities and policies for both mergers and other business practices across industries.
Kristen leverages her experience as a top government enforcer to represent clients in complex merger and non-merger investigations before the U.S. Department of Justice, the Federal Trade Commission, and international competition authorities, as well as in high-stakes appellate and civil litigation matters. In 2023, Kristen was honored as Global Competition Review’s “Dealmaker of the Year.” She has also been named a leading antitrust practitioner by Chambers USA, featured as one of Lawdragon’s “500 Leading Antitrust and Competition Lawyers” (2025-2026), and recognized in Global Competition Review’s Women in Antitrust (2025). Kristen is described by Chambers as a “very practical” and “excellent go-to advocate.” She brings this practical approach to helping clients navigate the increasingly complex antitrust enforcement environment, employing her deep experience with agency practice to achieve successful results in an efficient manner.
Since joining Gibson Dunn, Kristen has represented:
- VMware in securing global antitrust clearance of its $61 billion acquisition by Broadcom;
- Xylem in its acquisition of Evoqua;
- NewsCorp.’s Dow Jones subsidiary in its billion-dollar acquisition of assets from S&P Global and IHS Markit, proposed by the latter in connection with DOJ and foreign enforcers’ review of their global merger;
- Hershey Co. in its acquisitions of chocolate manufacturer Lily’s and pretzel maker Dots;
- General Electric in its acquisition of BK Medical;
- Welbilt in its proposed acquisition by Middleby and then in the successful topping bid acquisition by Ali Group; and
- Hologic in its acquisitions of Endomag, Biotheranostics and Bolder Surgical.
Kristen’s antitrust litigation experience includes representing:
- Marriott in defending class actions alleging information exchanges;
- Hill-Rom in defending a monopolization claim brought by a competitor;
- A major European financial institution in defending class actions alleging price fixing in European Government Bonds; and
- AT&T, as a non-party, in the DOJ’s investigations and lawsuits against Google.
Kristen brings exceptional experience and a practical approach to representing companies in non-public civil and criminal antitrust investigations. She has also served as a corporate compliance monitor, overseeing the adoption of rigorous competition-related controls at a corporation subject to a non-prosecution agreement with the Antitrust Division.
Prior to joining Gibson Dunn, Kristen twice received the U.S. Attorney General’s Distinguished Service Award. As DOJ Antitrust Division Appellate Section Chief, she was responsible for a team of more than a dozen professionals litigating appeals in the Division’s civil and criminal enforcement actions and participating as amicus curiae in private antitrust actions. While serving in the Antitrust Division, Kristen also helped to develop Division policies on a wide range of issues. She was a principal drafter of the agency’s Antitrust Guidance for Human Resources Professionals in 2016, she led the team revising the agency’s Antitrust Guidelines for International Enforcement and Cooperation in 2017 and was part of the small team of agency attorneys and economists that revised the Horizontal Merger Guidelines in 2010.
Kristen is senior fellow in George Washington University’s Competition and Innovation Lab, and speaks regularly on antitrust issues, including at programs for the U.S. Department of Justice, the American Bar Association, George Mason University, and the Association of American Law Schools.
She clerked for Judge Leonie M. Brinkema of the U.S. District Court for the Eastern District of Virginia from 2002 to 2003. She received her law degree, magna cum laude, in 2002 from Georgetown University Law Center, where she was elected to the Order of the Coif. Kristen earned a Bachelor of Arts degree with high honors from Swarthmore College in 1997.
Kristen is admitted to practice in the District of Columbia.
Christian is an associate in the London office of Gibson Dunn, and a member of the Antitrust and Competition Practice Group.
Christian advises on all matters of EU competition law, with particular expertise in overseeing global merger control and foreign direct investment filings and strategy.
Prior to joining Gibson Dunn, Christian was an associate in the Antitrust and Competition practice group at a leading Danish Law Firm. Christian is admitted to practice in Denmark.
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Amir C. Tayrani is a partner in Gibson Dunn’s Washington, D.C. office. He practices in the firm’s Litigation Department, is a member of the Appellate and Constitutional Law Practice Group and the Administrative Law and Regulatory Practice Group, and is Co-Chair of the Product Liability Practice Group. Amir was recently recognized by Benchmark Litigation as a “Future Star.” Earlier in his career, Amir was recognized twice as an Appellate Rising Star by Law360, which described Amir as “a major player in some of the nation’s recent, most high-profile lawsuits,” from the “Citizens United campaign finance case to the battle in California over Proposition 8.” Amir has also been consistently recognized in The Best Lawyers in America® guide for Appellate Practice since 2014. Amir has significant experience representing clients before the U.S. Supreme Court and other appellate courts. He has argued cases in federal and state appellate courts across the country, including in the U.S. Supreme Court. Amir has briefed 21 cases on the merits before the U.S. Supreme Court, including:
Amir also has an active administrative and regulatory practice. He regularly counsels clients in connection with matters pending before federal regulatory agencies — including the Financial Stability Oversight Council, the Securities and Exchange Commission, and the Environmental Protection Agency— and represents clients in litigation challenging agency action in the D.C. Circuit and other federal courts. In addition, Amir has extensive products-liability experience. He has defended clients in a range of industries — including chemicals, consumer products, medical devices, and aviation — against products-liability and mass-tort claims in trial and appellate proceedings. Amir has also advised insurers on products-liability defense and litigation strategy. Amir graduated from the Yale Law School in 2003, where he was Executive Editor of The Yale Law Journal. He served as a judicial clerk to the Honorable Diarmuid F. O’Scannlain of the United States Court of Appeals for the Ninth Circuit. Amir earned a B.A. degree summa cum laude in Political Science from California State University, Fullerton. He is licensed to practice in California and the District of Columbia, and before the Supreme Court of the United States and the United States Courts of Appeals for the Second, Third, Fourth, Fifth, Sixth, Seventh, Ninth, Tenth, Eleventh, D.C., and Federal Circuits.
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Emma Jiani Li is a litigation associate in the New York office of Gibson Dunn, where she primarily practices in the firm’s Antitrust and Competition and White Collar Defense and Investigations Practice Groups.
Emma has experience in a variety of complex litigation and government investigations, regularly representing clients in high-stakes antitrust and competition matters. She has worked on significant cases within the technology and cryptocurrency sectors, contributing to successful defenses and favorable outcomes. She also maintains an active pro bono practice representing asylum seekers.
Emma received her law degree from Duke University School of Law in 2022. During law school, she served as Co-President of the Asian Pacific American Law Students Association.
Emma is proficient in Mandarin Chinese.
Emma is admitted to practice in the State of New York.