Undisputed Champion-

Expectations for Tyson were extremely high, and he embarked on an ambitious campaign to fight all the top heavyweights in the world. Tyson defended his title against James Smith on March 7, 1987, in Las Vegas, Nevada. He won by unanimous decision and added Smith's World Boxing Association (WBA) title to his existing belt. 'Tyson mania' in the media was becoming rampant. He beat Pinklon Thomas in May with a knockout in the sixth round. On August 1 he took the International Boxing Federation (IBF) title from Tony Tucker in a twelve round unanimous decision. He became the first heavyweight to own all three major belts — WBA, WBC, and IBF — at the same time. Another fight in 1987 was in October that ended with a victory for Tyson by knockout in the seventh round, against 1984 Olympics Super Heavyweight Gold Medallist Tyrell Biggs. Also in 1987, Nintendo released the video game, Mike Tyson's Punch-Out!!, for its Nintendo Entertainment System.

Tyson had three fights in 1988. He faced Larry Holmes on January 22, 1988, and defeated the legendary former champion by a fourth round KO. This was the only knockout loss Holmes suffered in 75 professional bouts. In March, Tyson then fought contender Tony Tubbs in Tokyo, Japan, fitting in an easy two-round victory amid promotional and marketing work.

On June 27, 1988, Tyson faced Michael Spinks. Spinks, who had taken the heavyweight championship from Larry Holmes via a 15-round decision in 1985, had not lost his title in the ring but was not recognized as champion by the major boxing organizations. Holmes had previously given up all but the IBF title, and that was eventually stripped from Spinks after he elected to fight Gerry Cooney (winning by a 5th-round TKO) rather than IBF Number 1 Contender Tony Tucker, as the Cooney fight provided him a larger purse. However, Spinks did become the lineal champion by beating Holmes and many (including Ring magazine) considered him to have a legitimate claim to being the true heavyweight champion. The bout was, at the time, the richest fight in history and expectations were very high. Boxing pundits were predicting a titanic battle of styles, with Tyson's aggressive infighting conflicting with Spinks' skillful outfighting and footwork. The fight ended after 91 seconds when Tyson knocked Spinks out in the first round; many consider this to be the pinnacle of Tyson's fame and boxing ability. Spinks, previously unbeaten, would never fight professionally again.