He was known as "The Deputy Sheriff", Foster was one of the greatest light heavyweight champions in boxing history. He won the undisputed light heavyweight championship from Dick Tiger in 1968 via fourth round knockout, and went on to defend his crown fourteen times in total from 1968 to 1974. Foster challenged heavyweight kings Joe Frazier and Muhammad Ali during his career, but was knocked out by both fighters. He retired from professional boxing in 1978, at the age of 36.