Before his championship debut against the heavyweight champion Sonny Liston, Cassius Clay Jr., Will Smith taunts Liston and bursts out to an early lead, dominating the opening rounds. Midway through the bout, he complains of a burning sensation in his eyes — a moment that suggests Liston may have tried to cheat — and he says he cannot continue. His trainer Angelo Dundee keeps him in the fight, and when Clay regains his sight, he resumes control and drives Liston to quit before the seventh round. With this win, Clay becomes the second-youngest heavyweight champion after Floyd Patterson.
Clay's life expands beyond the ring as he moves into a broader civil-rights era circle. He spends time with Malcolm X and is invited to the home of Nation of Islam leader Elijah Muhammad, where he receives the name Muhammad Ali, Will Smith. His father Cassius Clay Sr. disapproves of the change. Ali then marries Sonji Roi, a former Playboy Bunny, though she is not Muslim and does not observe sex segregation. He travels to Africa and reconnects with Malcolm X, but later complies with Elijah Muhammad's wishes and cuts off contact with X, and he is deeply shaken by the assassination of Malcolm X.
Back in America, Ali fights Liston again and knocks him out in the first round. His marriage to Sonji ends in divorce as she objects to various obligations that Muslim women are asked to observe.
Ali refuses to be drafted for the Vietnam War and is stripped of his boxing license, passport, and title, later sentenced to five years in prison. After marrying Belinda Boyd, then 17 years old, and taking a three-year hiatus from boxing, his conviction is overturned in Clay v. United States. In his comeback, he faces Jerry Quarry and wins by technical knockout in three rounds. He aims to regain the heavyweight crown by challenging Joe Frazier. In the Fight of the Century, Frazier dominates and wins by decision, marking Ali's first professional loss. Frazier would later lose the title to George Foreman.
Foreman and Ali travel to Kinshasa, Zaire, for the Rumble in the Jungle. There, Ali encounters Veronica Porché and begins an affair with her. After reports of the affair leak, Belinda travels to Zaire to confront him. Ali says he cannot decide whether he loves Veronica but remains focused on his upcoming shot at the title. For much of the fight, Ali employs the famous rope-a-dope tactic, leaning back against the ropes to tire Foreman, then delivers a decisive knockout to reclaim the Heavyweight Championship.
