In 1982, Simons founded Renaissance Technologies Corporation, a private investment firm based in New York with over $30 billion under management; Simons is still at the helm, as president, of what is now one of the world's most successful hedge funds. Simons earned an estimated $2.8 billion in 2007 , $1.7 billion in 2006, $1.5 billion in 2005, (the largest compensation among hedge fund managers that year) and $670 million in 2004. With an estimated current net worth of around $5.5 billion, he is ranked by Forbes as the 57th-richest person in America. He was named by the Financial Times in 2006 as the "smartest" billionaire.
Simons shuns the limelight and rarely gives interviews, citing Benjamin the Donkey in Animal Farm for explanation: "God gave me a tail to keep off the flies. But I'd rather have had no tail and no flies.
Jim Simons, the grandson of a shoe factory owner in Massachusetts, received his bachelor's degree in mathematics from the Massachusetts Institute of Technology (MIT) in 1958, and his PhD, also in mathematics, from the University of California, Berkeley in 1962 at the age of 23. From 1961 to 1964, he taught mathematics at MIT and Harvard University. Between 1964 and 1968, he was on the research staff of the Communications Research Division of the Institute for Defense Analyses (IDA). In 1968, he was appointed chairman of the math department at Stony Brook University transforming it into one of the top ten in the nation.
In 1976, Simons won the American Mathematical Society's Oswald Veblen Prize in Geometry, for work that involved a recasting of the subject of area minimizing multi-dimensional surfaces and characteristic forms. This resulted in his proof of the Bernstein conjecture up to real dimension 8, and an improvement of a certain "regularity" result of Wendell H. Fleming on a generalized Plateau's problem.
Renaissance employs many specialists with non-financial backgrounds, including mathematicians, physicists, astrophysicists and statisticians. The firm's latest fund, the Renaissance Institutional Equities Fund (RIEF), is designed to handle upwards of $100 billion. The RIEF has historically trailed the firm's more well-known Medallion fund, a separate fund that only contains the personal money of the firm's executives
Simons was the IAFE's (International Association of Financial Engineers) FEOY (Financial Engineer of the Year) for 2006. In 2007 he was estimated to have personally earned $1.7bn.
In a statement released to shareholders, the fund announced it had sustained losses of up to 7% in the wake of the 2007 Subprime mortgage financial crisis but managed to end the month of August with a positive performance of +0.7%
Simons and his second wife, Marilyn Hawrys Simons, co-founded the Paul Simons Foundation, a charitable organization which supports projects related to education and health, in addition to scientific research. In memory of his son Paul, he established Avalon Park, a nature preserve in Stony Brook. 34-year-old Paul was killed by a car in 1996 while riding a bicycle near their home. 23-year-old son Nick drowned in 2003 while on a trip to Bali in Indonesia. Nick had worked in Nepal and the Simonses have become large donors to Nepalese healthcare through the Nick Simons Institute. Jim Simons also founded Math for America.
In early 2006, he led a group of directors of Renaissance Technologies Corporation and of Brookhaven Science Associates in donating $13 million to fund a budget shortfall of the Brookhaven National Laboratory that would have shut down the operations of the Relativistic Heavy Ion Collider for 2006.
Also in 2006 Simons donated $25 million to Stony Brook University through the Stony Brook Foundation. The gift is intended to benefit the Mathematics and Physics departments at the university.
On February 27, 2008, Gov. Eliot Spitzer announced a $60 million donation by the Simons Foundation to found the Simons Center for Geometry and Physics at Stony Brook, the largest gift to a public university in New York state history.
On June 11, 2003, the Simons Foundation hosted its first "Panel on Autism Research" in New York City, a day-long event highlighting research into the causes of autism, the accurate genomic mapping of autism, and in the study of the biochemical mechanisms that occur in people with autism. Attendees included David Amaral, Dr. Eric Courchesne, Dr. Nathaniel Heinz, Tom Insel, MD, Catherine Lord, PhD, Dr. Fred Volkmar and Dr. Paul Greengard. The Simons Foundation recently gave $10 million to two researchers at the Yale University Child Study Center to study genetic influences on autism.