Hugh Everett III (1930 – 1982) was an American physicist who first proposed the many-worlds interpretation of quantum physics, which he called his "relative state" formulation.

He left physics after completing his Ph.D., discouraged at the lack of response to his theories from other physicists. He worked as a defense analyst and a consultant, became a multimillionaire, and did research on improving the effectiveness of nuclear weapons.

Everett was born in Maryland and raised in the Washington, D.C. area, and lived in Fairfax County, Virginia for most of his professional career.

After World War II, Everett was stationed in West Germany and visited East Germany during the Cold War.

Everett founded several companies in the 1960s and 1970s, including the defense contracting companies Lambda Corporation and Monowave Corporation (along with Elaine Tsiang, a former employee of Everett's at Lambda Corporation). Through these ventures, Everett became a millionaire.

Currently, of the companies Everett founded, only Monowave Corporation still exists (now in Seattle, Washington State) and is still run by Elaine Tsiang.

He was also the father of Mark Oliver Everett, a.k.a. E, the lead singer of the band eels.