Mike Tyson grows up a troubled youth, who aspires to become a professional boxer. Manager and trainer Cus D'Amato begins turning the young Tyson into an undefeated fighter. However, Tyson becomes a difficult pupil who is often exposed, and slacks off during his training.
D'Amato surrounds Tyson with boxing managers Jimmy Jacobs, Bill Cayton, and trainer Kevin Rooney to help rebuild the boxer's life. D'Amato tells Tyson that as long as he keeps good people nearby, they can keep him out of trouble.
Tyson quickly rises through the ranks, but becomes upset when D'Amato's health deteriorates, and he dies. Jacobs then takes over as Tyson's manager. In 1986, Tyson takes part in the match against Trevor Berbick in Las Vegas at the World Boxing Council heavyweight championship. At twenty years of age, Tyson wins, and becomes the youngest champion in boxing history. In 1987, the match against Tony Tucker takes place, in which Tyson wins, and retains his title.
Tyson marries his pregnant girlfriend, actress Robin Givens. The event is followed by the sad news of Jacobs' death due to leukemia. Cayton takes on the job of managing Tyson. Don King seeks Tyson with an offer to manage his career. Tyson declines, but decided to hire King as his new promoter instead. A battle of words flies between King, Givens, and Cayton in the media, as they accuse each other of swindling Tyson.
When Robin suffers a miscarriage, Tyson slacks off during his training. Rooney, in a fit of frustration, tells him that Robin was never pregnant to begin with. Tyson in response knocks out two of his training fighters.
In 1988, the match against Michael Spinks takes place. Before the match, Cayton learns that he has been fired. Tyson defeats Spinks and everyone cheers on, but Cayton and Rooney are not on the same page. During a television interview with Barbara Walters, Robin unintentionally embarrasses Tyson with his mental health issues.
Meanwhile, police arrive at the home where Robin lives, and where Tyson is throwing a temper tantrum. Robin tells the press that Tyson has become an emotionally abusive husband. She moves out and files for divorce.
In Tokyo, on February 11, 1990, the match against Buster Douglas takes place. Tyson fights hard, but the match ends with Douglas victorious over Tyson by knockout.
In 1991, Tyson is brought to trial for raping beauty pageant contestant, Desiree Washington. He is convicted of rape and criminally deviant conduct, and sentenced to six years in prison, which is served at the Indiana Youth Center. Rooney files a suit against Tyson for civil damages. Upon release in 1995, Tyson announces that he will attempt a comeback. King remains his promoter, but is scheduled to stand trial for insurance fraud.
