John Albert Overdeck (born 1969) is an American billionaire hedge fund manager. Overdeck is the co-founder and co-chairman of Two Sigma Investments, a New York City-based hedge fund that uses a variety of technological methods, including artificial intelligence, machine learning, and distributed computing for its trading strategies. In 2016, Overdeck reported $375 million in earnings and as of May 2017, Two Sigma Investments has $41 billion in assets under management.

In March 2019, he was named one of the highest-earning hedge fund managers and traders by Forbes.

Overdeck is the son of Dr. John M. Overdeck of Columbia, Maryland, a retired senior mathematician at Fort Meade, Maryland, for the National Security Agency, and the late Betsey Lombard Overdeck, who was a director of Computer Sciences Corporation.

Overdeck went to Wilde Lake High School in Columbia, Maryland. In 1986, he was an International Mathematics Olympiad silver medalist. He then earned a bachelor's degree in mathematics and a master's degree in statistics, both from Stanford University.

Prior to co-founding Two Sigma Investments, Overdeck was a managing director at D.E. Shaw & Co., and a vice president at Amazon.com.

Overdeck founded Two Sigma Investments in 2001 with David Siegel and Mark Pickard, who is now retired. The company's main office is in New York City with branch offices in Houston, London, and Hong Kong. In January 2015, the firm had $34.21 billion in assets under management and as of May 2017, the firm had $41 billion.

Two Sigma Investments also operates a market-making business, owns a Bermuda reinsurance company, and runs a venture capital arm.

In March 2017, Overdeck ranked 9th on Forbes' Highest-Earning Hedge Fund Managers.