How Marilyn built the fortune
The Simons family fortune was created by Jim Simons, a mathematician who founded the investment firm Renaissance Technologies and died in May 2024. Marilyn Simons, his wife of more than four decades, became the main holder of the family's wealth after his death, alongside large amounts already committed to their charitable foundation.
Renaissance applied mathematics, statistics and computing to financial markets at a time when most investors relied on judgment and fundamental research. Jim Simons hired mathematicians, physicists and computer scientists rather than traders, and the team built models that found small, repeatable patterns in price data. The firm's flagship Medallion Fund, launched in 1988, produced some of the strongest long-term returns ever recorded in investing. Since the 1990s Medallion has been open only to Renaissance employees and insiders, and it charges very high fees, so its gains flowed largely to the firm's owners and staff.
Renaissance also manages funds for outside investors, which have had more ordinary results. The family's fortune reflects decades of profits from Medallion, Jim Simons's ownership stake in Renaissance and the investment of those gains over many years. Because so much was donated to the Simons Foundation during his lifetime, a significant share of the wealth created by the firm now sits in philanthropy rather than in personal accounts.
Companies and holdings
The family's financial interests are tied mainly to:
- Renaissance Technologies, the quantitative investment firm based in East Setauket on Long Island, New York, which runs the Medallion Fund and funds for outside clients
- A portfolio of investments built from distributions over several decades
Jim Simons stepped down as chief executive of Renaissance in 2010 and retired as chairman in 2021, and the firm is run by a management team drawn from its scientific staff. Marilyn Simons does not have a management role at Renaissance. Her own work is concentrated on the foundation the couple created, where she has been the central figure for three decades.
Early life and career
Marilyn Hawrys Simons studied at Stony Brook University, part of the State University of New York, where she earned a bachelor's degree and later a doctorate in economics. Stony Brook was also where she met Jim Simons, who chaired the university's mathematics department in the 1970s before leaving academia for finance. They married in 1977, and the university remained a central part of their lives for decades afterwards.
In 1994, as Renaissance was becoming highly profitable, the couple set up the Simons Foundation. She served as its president for many years, guiding its growth from a modest family foundation into one of the largest private funders of basic science in the United States, and she later became its chair. Under her leadership the foundation moved from writing checks to outside researchers toward running its own scientific programs, hiring staff scientists and building research groups in New York. That shift made the foundation unusual among private funders, since few philanthropies employ their own research scientists on such a scale.
Philanthropy and public life
The Simons Foundation is the focus of Marilyn Simons's public life. It supports research in mathematics, physics, computer science and the life sciences, and it runs the Flatiron Institute in New York, an internal research center founded in 2016 that develops computational methods for science. Its autism research initiative, begun in 2003, has become one of the largest private funders of autism science. The foundation also supports science education and outreach and helped build the Simons Observatory in Chile.
The couple signed the Giving Pledge in 2010. Stony Brook University has been one of their largest beneficiaries: in 2023 the Simons Foundation committed 500 million dollars to the university's endowment, among the largest gifts ever to a US public university. Marilyn Simons keeps a low public profile, speaking mainly through the foundation's work. She has also supported Math for America, a program founded by Jim Simons in 2004 that pays stipends to outstanding mathematics and science teachers in public schools, helping them stay in the profession.