Title: Buster Douglas
Content: Buster Douglas James "Buster" Douglas (born April 7, 1960) is an American former professional boxer who competed from 1981 to 1990, and 1996 to 1999. He is best known for his stunning upset of Mike Tyson on February 11, 1990, in Tokyo to win the undisputed heavyweight title. At the time Tyson was undefeated and considered to be the best boxer in the world, as well as one of the most feared heavyweight champions in history due to his domination of the division over the previous three years. The only casino to make odds for the fight (all others declining

Title: Buster Douglas
Content: HBO studios. Although the IBF immediately recognized Douglas as its champion, the WBA and WBC initially refused due to Tyson's protest. However, Tyson withdrew his protest four days later amid worldwide public outcry and demands from boxing commissions around the world, and Douglas was officially recognized as undisputed heavyweight champion. While still champion, Douglas appeared on the February 23, 1990 episode of the World Wrestling Federation's "The Main Event", as special guest referee for a rematch between Hulk Hogan and "Macho Man" Randy Savage. Originally, Tyson was scheduled to be the guest referee, but following the upset, the WWF scrambled

Title: Mike Tyson vs. Frank Bruno
Content: knockout, becoming the new undisputed heavyweight champion in the process. Tyson then embarked on a comeback in hopes of securing a championship match with either Douglas or Evander Holyfield, who were scheduled to face each other for the undisputed heavyweight title on October 25, 1990. Tyson would go on to defeat Henry Tillman, Alex Stewart and Donovan Ruddock twice before being arrested and sentenced to prison for rape. When Tyson was released in 1995, he returned to boxing and easily defeated journeymen Peter McNeeley and Buster Mathis, Jr. This would set up a rematch with Bruno for Bruno's newly won

Title: Mike Tyson
Content: Mike Tyson Michael Gerard Tyson (born June 30, 1966) is an American former professional boxer who competed from 1985 to 2005. He reigned as the undisputed world heavyweight champion and holds the record as the youngest boxer to win a heavyweight title at 20 years, four months and 22 days old. Tyson won his first 19 professional fights by knockout or stoppage, 12 of them in the first round. He won the WBC title in 1986 after stopping Trevor Berbick in the second round, and added the WBA and IBF titles after defeating James Smith and Tony Tucker in 1987.

Title: Heavyweight unification series
Content: Heavyweight unification series The heavyweight unification series, also known as the Heavyweight World Series, was a sequence of professional boxing matches held in 1986 and 1987 to crown an undisputed champion of the heavyweight class. The series was produced by HBO Sports and promoted by Don King. It ended with Mike Tyson as undisputed champion, holding the championship belts of the International Boxing Federation, World Boxing Association, and World Boxing Council. Prior to the series, the last undisputed heavyweight champion had been Leon Spinks, who won the championship in his 1978 victory over Muhammad Ali. Spinks had been stripped of

Question: Who was the last undisputed boxing world heavyweight champion before Mike Tyson?
Answer: Leon Spinks