Muhammad Ali began training at 12 years old. He became World Heavyweight Champion in 1964 aged just 22.
Ali remains the only three-time world heavyweight champion. He won the title in 1964, 1974, and 1978.
Between February 25, 1964 and September 19, 1964 Muhammad Ali reigned as the undisputed heavyweight boxing champion.
Here are some of his most memorable moments in the ring:
Ali (still known as Cassius Clay at the time) v. Henry Cooper in 1963.
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The fight was Ali's first fight as a pro outside of the United States. Henry Cooper was the reigning Commonwealth and British heavyweight champion.
Late in the fourth round Ali was floored by Cooper. Cooper eventually lost but was one of only three men to ever drop Ali in his 61-fight career.
World heavyweight champion — Ali v. Sonny Liston in 1964
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Liston was convinced he would beat Ali within the first two rounds and trained minimally for the bout in Miami Beach, Florida. At the time Ali was disliked by the press and widely dismissed.
The fight between the pair was one of the most anticipated, watched and controversial fights in the sport's history.
Ali won when Liston gave up at the opening of the seventh round. When he realized he had won, Ali ran to the ropes and shouted at the media "Eat your words!"
"I'm the greatest!" he yelled. "I shook up the world." Ali took the title of world heavyweight champion.
The Rematch — Ali v. Liston in 1965
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Ali knocked out Liston in the first round of their rematch in Lewiston, Maine — there was significant debate over whether Liston took a dive. Ali retained his title.
The Fight Of The Century — Ali v. Joe Frazier in 1971
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Ali faced new champion Joe Frazier at Madison Square Garden in 1971.
After his ban from boxing for refusing to be drafted during the Vietnam War, Ali was not in top form and Frazier pulled a left hook in 15th round. Ali got up but lost a unanimous decision.
The Rumble in the Jungle — Ali v. George Foreman in 1974
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Very few expected Ali to beat George Foreman during their bout in in Kinshasa, Zaire (now the Democratic Republic of the Congo).
But after six rounds Foreman was exhausted and with 20 seconds remaining of the eighth, Ali unfurled a chain of punches and Foreman fell.
On commentary David Frost announced: “The great man has done it! This is the most joyous scene ever seen in the history of boxing!”
Thrilla in Manila — Ali v. Joe Frazier in 1975
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The third and final boxing match between Ali and Joe Frazier and was held at the Araneta Coliseum in Quezon City, Metro Manila in the Philippines.
Ali won by technical knockout after Frazier's chief second, Eddie Futch, conceded the fight prior to the 15th round.
The fight is often ranked as one of the best in the sport's history and was the culmination of a three-bout rivalry between the two fighters that Ali won, 2–1.
Three-time heavyweight champion — Ali v. Spinks in 1978.
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Ali, 36, became the first three-time heavyweight champion in history upon beating Spinks in New Orleans.
Spinks had taken the world title off Ali earlier the year winning a decision over 15 rounds in Las Vegas.
The rematch was the final peak of Ali's career. He retired the following June.