As Muhammad Ali approaches his epic first fight with Joe Frazier in 1971, we look back on his childhood as Cassius Clay in Louisville, KY; his amateur career, which culminated in a Golden Gloves triumph and a 1960 Olympic Gold Medal in the light-heavyweight division; and his ascension to heavyweight champion, when he "shocked the world" in 1964 as an arrogant 22-year-old by beating Sonny Liston. After converting to Islam and forging close ties with Malcolm X and Elijah Muhammad, Cassius changed his name to Muhammad Ali, beat Liston again, and defended his championship seven more times before being stripped of his title in 1967 for refusing to be drafted into the Army to fight in Vietnam. Exonerated after three long years, Ali returned to the ring in 1970, where he pummeled Jerry Quarry and Oscar Bonavena before agreeing to a "Fight of the Century" in New York's Madison Square Garden against the unbeaten Joe Frazier.

Determined to avenge his defeat to Joe Frazier, Ali builds a rustic training camp in Deer Park, PA, and goes on to defeat a parade of contenders before losing to Ken Norton in 1973. The loss jeopardizes a Frazier rematch, but a recommitted Ali beats Norton in a second bout, setting up an encore with Frazier, who was dethroned by George Foreman earlier that year. This time, Ali beats his nemesis, with his reward being the 1974 "Rumble in the Jungle" with Foreman in Zaire. Against all odds, Ali KOs an exhausted Foreman to regain the heavyweight title, and becomes an idol around the world. Another epic victory over Frazier, 1975's "Thrilla in Manilla," follows, but the toll of so many brutal fights starts to show. After several up-and-down bouts (and retirements), Ali vows to return to the ring, and in December 1981 he loses badly to Trevor Berbick. Finally, Ali retires for good and The Greatest travels the world as a goodwill ambassador.