Leon Spinks was an American professional boxer who competed from 1977 to 1995. In only his eighth professional fight, he won the undisputed heavyweight championship in 1978 after defeating Muhammad Ali in a split decision, in what is considered one of the biggest upsets in boxing history. Spinks was later stripped of the WBC title for facing Ali in an unapproved rematch seven months later, which he lost by a unanimous decision.

In boxing, the undisputed champion of a weight class is the boxer who simultaneously holds world titles from all recognized major organisations by each other and the International Boxing Hall of Fame. There are currently four major sanctioning bodies: WBA, WBC, IBF and WBO. There were many undisputed champions before the number of major sanctioning bodies recognizing each other increased to four in 2007, but there have only been 19 boxers to hold all four titles simultaneously.