Gilead Sciences vs Regeneron: Founders, CEOs and History
Gilead Sciences was founded in 1987 by Michael L. Riordan and is led by Daniel P. O'Day. Regeneron was founded in 1988 by Leonard S. Schleifer, George D. Yancopoulos and is led by Leonard S. Schleifer.
Company facts
Gilead Sciences
- Founded
- 1987
- Headquarters
- Foster City, California
- Current CEO
- Daniel P. O'Day
- Employees
- 17,000
Regeneron
- Founded
- 1988
- Headquarters
- Tarrytown, New York
- Current CEO
- Leonard S. Schleifer
- Employees
- 15,410
Founders
Gilead Sciences
Michael L. Riordan
Michael Riordan founded Gilead in Foster City, California, in 1987. Before that he trained in medicine and worked in venture capital at Menlo Ventures, which provided early funding.
Regeneron
Leonard S. Schleifer
Leonard S. Schleifer founded Regeneron in 1988 and has led it as CEO since then, making him one of the longest-serving founder-CEOs in the S&P 500. He is also President and Board co-Chair.
George D. Yancopoulos
George D. Yancopoulos joined Regeneron in 1989 as its founding scientist and serves as Board co-Chair, President and Chief Scientific Officer.
CEOs and their tenures
Gilead Sciences
- Michael Riordan1987–1996
Chief Executive Officer
He successfully navigated the brutal early stages of biotech funding, taking the company public in 1992 and establishing its foundational viral research culture.
Source - John C. Martin1996–2016
Chief Executive Officer
As CEO for two decades, he took Gilead from a small biotech startup to a pharmaceutical behemoth, generating tens of billions in revenue from Truvada and Sovaldi.
Source - John F. Milligan2016–2018
Chief Executive Officer
During his nearly three decades at Gilead, he helped build the company's HIV franchise before orchestrating the monumental financial success of the HCV cures.
Source - Daniel P. O'Day2019–present
Chairman and Chief Executive Officer
O'Day's leadership has transformed Gilead from a specialized virology company into a diversified, global biopharmaceutical leader.
Source
Regeneron
- Christopher Fenimore
Executive Vice President, Finance and Chief Financial Officer
Oversees finance and capital allocation, including share repurchases and the dividend.
Source - Leonard S. Schleifer, M.D., Ph.D.1988–present
Founder, Board co-Chair, President and CEO
Has led Regeneron since 1988, from platform research to a company with $14.34 billion in FY2025 revenue.
Source - George D. Yancopoulos, M.D., Ph.D.1989–present
Co-Founder, Board co-Chair, President and Chief Scientific Officer
Runs Regeneron Research and the scientific portfolio.
Source
Timeline: Gilead Sciences and Regeneron side by side
1987Gilead Sciences
Founding of Gilead Sciences
Michael L. Riordan founded the company, originally called Oligogen, in Foster City, California, to develop antisense and antiviral therapies.
1988Regeneron
Regeneron is founded
Leonard S. Schleifer founded Regeneron in New York in 1988; George D. Yancopoulos joined in 1989.
1991Regeneron
Regeneron goes public
The company listed on Nasdaq and funded a long period of platform research before becoming a commercial biotech.
1992Gilead Sciences
Initial Public Offering
Gilead went public on Nasdaq, giving it the capital to keep developing antiviral drugs.
2001Gilead Sciences
Approval of Viread
The FDA approved Viread (tenofovir disoproxil fumarate), the nucleotide analog that became the backbone of Gilead's HIV franchise.
2003Gilead Sciences
Acquisition of Triangle Pharmaceuticals
Gilead acquired Triangle Pharmaceuticals, gaining emtricitabine, which it combined with tenofovir to create Truvada.
2006Gilead Sciences
Atripla Approved
The FDA approved Atripla, the first once-daily single-tablet HIV regimen, in July 2006.
2008Regeneron
Arcalyst becomes Regeneron's first approved medicine
Arcalyst validated Regeneron's trap-technology work and showed that the platform could produce approved therapies.
2011Gilead Sciences
Acquisition of Pharmasset
Gilead acquired Pharmasset for about $11 billion, gaining sofosbuvir, the basis of hepatitis C cures Sovaldi and Harvoni.
2011Regeneron
EYLEA approval transforms the company
EYLEA gave Regeneron a major ophthalmology franchise and moved the company into large-scale commercial operations.
2013Gilead Sciences
Sovaldi Approved
The FDA approved the hepatitis C drug Sovaldi in December 2013.
2017Gilead Sciences
Acquisition of Kite Pharma
Gilead acquired Kite Pharma for about $11.9 billion, adding the CAR-T therapy Yescarta.
2017Regeneron
Dupixent is approved
Dupixent, developed with Sanofi, became a global immunology growth engine and a central part of Regeneron's collaboration economics.
2020Gilead Sciences
Acquisition of Immunomedics
Gilead acquired Immunomedics for about $21 billion, adding the Trop-2 antibody-drug conjugate Trodelvy.
2020Regeneron
COVID-19 Antibody Authorization
The FDA granted emergency use authorization to Regeneron's COVID-19 antibody treatment in November 2020.
2022Regeneron
Checkmate Pharmaceuticals deal expands immuno-oncology
Regeneron agreed to acquire Checkmate Pharmaceuticals for about $250 million to add the investigational TLR9 agonist vidutolimod.
2023Regeneron
Decibel Therapeutics acquisition closes
Regeneron completed its acquisition of Decibel Therapeutics and added hearing-loss gene-therapy programs, including investigational DB-OTO in Phase 1/2 CHORD. It was not an approved therapy.
2023Regeneron
EYLEA HD is approved
The FDA approved EYLEA HD (aflibercept 8 mg) in August 2023, giving Regeneron a longer-dosing successor to EYLEA.
2024Gilead Sciences
PURPOSE 1 Trial Results
Twice-yearly lenacapavir showed zero HIV infections among women in the PURPOSE 1 prevention trial.
2024Regeneron
Regeneron Cell Medicines is formed
Regeneron acquired full development and commercialization rights to 2seventy bio's cell-therapy platforms and pipeline programs.
2025Gilead Sciences
Yeztugo Approval and FY2025 Results
The FDA approved Yeztugo (lenacapavir) in June 2025 as the first twice-yearly HIV PrEP option. Gilead finished 2025 with $29.4 billion in revenue and $14.3 billion in Biktarvy sales.
2025Regeneron
Revenue reaches $14.34 billion
Regeneron reported FY2025 revenue of about $14.34 billion, with Dupixent growth offsetting pressure in the original EYLEA franchise.
2026Gilead Sciences
Arcellx, Tubulis and Ouro Acquisitions
Gilead closed acquisitions of Arcellx (April, about $7.8 billion implied equity value), Tubulis (May, $3.15 billion upfront) and Ouro Medicines ($1.675 billion upfront).
2026Regeneron
Q2 2026 revenue rises 17% to $4.3 billion
Dupixent global sales reached $6.0 billion and the Sanofi development balance was fully repaid by the end of the quarter.
Acquisitions
Gilead Sciences
- Arcellx, Inc.2026$7.8B
- Tubulis GmbH2026$3.1B
- Ouro Medicines2026$1.7B
- CymaBay Therapeutics2024$4.3B
- Immunomedics, Inc.2020$21B
- Forty Seven, Inc.2020$4.9B
Regeneron
- 2seventy bio platforms and pipeline rights2024$5M
- Decibel Therapeutics2023$109M
- Checkmate Pharmaceuticals2022$250M
Questions about Gilead Sciences vs Regeneron
Who is the CEO of Gilead Sciences, Inc. and Regeneron Pharmaceuticals, Inc.?
Gilead Sciences, Inc. is led by Daniel P. O'Day and Regeneron Pharmaceuticals, Inc. is led by Leonard S. Schleifer. Both serve as the top executive responsible for the company's strategy, operations, and financial performance.
When was Gilead Sciences, Inc. founded vs Regeneron Pharmaceuticals, Inc.?
Gilead Sciences, Inc. was founded in 1987 — 1 year before Regeneron Pharmaceuticals, Inc., which was founded in 1988. Gilead Sciences, Inc.'s longer operating history gives it a deeper track record but also potentially more institutional inertia compared to the younger Regeneron Pharmaceuticals, Inc..
How many employees does Gilead Sciences, Inc. have compared to Regeneron Pharmaceuticals, Inc.?
Gilead Sciences, Inc. employs approximately 17,000 people, while Regeneron Pharmaceuticals, Inc. employs approximately 15,410. Gilead Sciences, Inc. has the larger workforce at 17,000 employees, compared to Regeneron Pharmaceuticals, Inc.'s 15,410. A higher headcount does not necessarily imply greater efficiency — it often reflects differences in business model (e.g., manufacturing vs. software).
Where are Gilead Sciences, Inc. and Regeneron Pharmaceuticals, Inc. headquartered?
Both Gilead Sciences, Inc. and Regeneron Pharmaceuticals, Inc. are headquartered in United States. Their local rules and tax obligations may still differ.
Who founded Gilead Sciences, Inc. and Regeneron Pharmaceuticals, Inc.?
Gilead Sciences, Inc. was founded by Michael L. Riordan. Regeneron Pharmaceuticals, Inc. was founded by Leonard S. Schleifer, George D. Yancopoulos.
Which company has a longer operating history — Gilead Sciences, Inc. or Regeneron Pharmaceuticals, Inc.?
Gilead Sciences, Inc. has been operating for approximately 39 years, making it the more established of the two companies. Regeneron Pharmaceuticals, Inc. has been in operation for around 38 years. A longer operating history often signals greater institutional resilience and brand recognition, though it can also mean slower adaptation to new market conditions.
Figures come from each company's filings and the sources linked beside them. Amounts reported in another currency are shown in US dollars at an approximate rate and marked with ~. Back to the Gilead Sciences vs Regeneron overview