But the three-time heavyweight champion of the world was much more than just a boxer. With his wit, eloquence and infectious bravado, he charmed the world and proved an inspiration to many. And, proving his courage was not just physical, he established himself as a significant figure in the civil rights movement.
Conscientiously objecting to the Vietnam War made him unpopular at the time and earned him a three-and-a-half-year ban from his sport. Similarly, when he changed his name from Cassius Clay to Muhammad Ali after joining the Nation of Islam, he became America's highest profile Muslim in what was a deeply Christian country.
Ali's death was confirmed by his family in a statement who said they "would like to thank everyone for their thoughts, prayers and support".
On Saturday a family spokesman confirmed Ali had died of septic shock “due to unspecified natural causes.”
He had battled Parkinson's disease for more than 30 years and was admitted to hospital in Phoenix, Arizona, with a respiratory condition earlier in the week. The funeral will take place in Ali's home town of Louisville, Kentucky.
Hailed as “The Greatest”, after the world largely accepted what he had told them for years, he was admired by millions for his courage and bravery, which was reflected in the tributes that poured in.
President Barack Obama led tributes in a statement from himself and the First Lady.
Mr Obama said Ali "shook up the world" and credited him as always having "fought for what was right" even after his boxing career ended and his illness with Parkinson's begun.
“Later, as his physical powers ebbed, he became an even more powerful force for peace and reconciliation around the world," Mr Obama said.
"We saw a man who said he was so mean he’d make medicine sick reveal a soft spot, visit children with illness and disability around the world, telling them they, too, could become the greatest.
"We watched a hero light a torch, and fight his greatest fight of all time on the world stage once again, a battle against the disease that ravaged his body, but couldn’t take the spark from his eyes.”
Former heavyweight boxer George Foreman, who was Ali's defeated opponent in the famous 1974 'Rumble in the Jungle fight' said: “A part of me slipped away, the greatest piece."
Other boxers, including Mike Tyson, Frank Bruno and Lennox Lewis, also marked his passing on Twitter.
Known as the Louisville Lip for his outspoken comments, he made a habit of standing up to authority. Ali repeatedly railed against racism in the 1960s, as well as the Vietnam War. He would later go on to meet dozens of world leaders and become one of the most recognisable faces on the planet.
Civil rights campaigner Reverend Jesse Jackson Snr summed up what Ali was to many.
"He became a champion inside the ring and a hero outside. Champion because he won the boxing matches, hero because he stood up against the war in Vietnam," he told BBC Radio Four's Today programme.
Always the entertainer, Ali's career was marked by several famous interviews such as the four he gave to Michael Parkinson, who described Ali as the "most remarkable man" he had ever met.
Today, Parkinson said Ali was simply "extraordinary".
But he added: "We mustn't deify him at all ... he was a man of many flaws, but he was a man of great genius, great charm, great humour and he was, in his quiet moments, fascinating."
Once asked about his preferred legacy, Ali said: “I would like to be remembered as a man who won the heavyweight title three times, who was humorous and who treated everyone right.
"As a man who never looked down on those who looked up to him ... who stood up for his beliefs ... who tried to unite all humankind through faith and love.
“And if all that's too much, then I guess I'd settle for being remembered only as a great boxer who became a leader and a champion of his people. And I wouldn't even mind if folks forgot how pretty I was.”
Ali has suffered from Parkinson's for three decades and trembled badly while lighting the Olympic torch in 1996 in Atlanta. At his last public appearances, he looked increasingly frail, including on 9 Apil when he wore sunglasses and was hunched over at the annual Celebrity Fight Night dinner in Phoenix, which raises funds for Parkinson's treatment.
Ali is survived by his fourth wife Lonnie – whom he married in 1986 – and nine children, many of whom were reported to have flown to their father's bedside on Thursday and Friday.
Reuters contributed to this report
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