The three-time former world champion, widely considered among the greatest heavyweights in the history of the sport, has passed away after being taken to an Arizona hospital with respiratory issues.
Ali had suffered for 35 years with Parkinson’s disease, having been diagnosed three years after his retirement in 1981.
The last several years has seen the former boxer’s public appearances diminish as he continues to battle the crippling condition. Recently he was forced to cancel a planned trip to London to open an exhibition on his life.
Two years ago reports surfaced the Olympic gold medalist’s health had deteriorated so much he was unable to speak. It led him to miss the premiere in Hollywood of the new I Am Ali movie, due to his frailty.
Several days later however he took to Twitter in attempt to reassure fans he was alright posting a picture of himself smiling alongside two women at the Boar's Head in Charlottesville, Virginia.
However, prior to his admittance to hospital, Ali hadn't been seen publicly since April, when he attended a Celebrity Fight Night in Phoenix.
He was taken to hospital on Thursday suffering from respiratory issues, after guests at his house in Scottsdale failed to wake him.
At the time sources said: “He wasn’t responding.
“He went to bed night, but didn’t wake up in the afternoon or evening the next day. He was sleeping for 24 hours.'
“They thought he might be too exhausted.”
However, his condition decreased on Friday and he was put on a life support machine with his respiratory problem complicated by his Parkinson's.
Ali lifted the world heavyweight title three times, with his first title coming at the age of 22, when Ali, then known by his birth name of Cassius Clay, shocked the world with his victory over Sonny Liston, who failed to answer the bell at the start of the seventh round after being comprehensively overwhelmed in the sixth.
Also known widely as The Greatest, he changed his name and converted to Islam ahead of the pair’s rematch in 1965, where he beat Liston inside the first round.
He was stripped of his world titles in 1966 and refused to serve in the US army, during the Vietnam War, famously declaring “I ain’t got no quarrel with them Viet Cong - no Viet Cong ever called me n*”, and was systematically denied a boxing licence and stripped of his passport.
His refusal saw him convicted of draft evasion - after only 21 minutes of deliberation from the jury - seeing Ali banned from boxing for three years and sentenced to five in prison.
He did not box between March 1967 and October 1970, before eventually seeing his conviction overturned by the Supreme Court in 1971, missing arguably his peak years (25-29). During his time away from the ring he spoke at colleges across the nation, criticising the war in Vietnam and advocating African-American pride, as well as racial justice.
He returned to the ring against Jerry Quarry in October 1970, winning in three rounds, before going on to endure legendary rivalries with both Joe Frazier and George Foreman, gifting the world two of the greatest fights ever: The Rumble in the Jungle (against Foreman) and The Thrilla in Manila (versus Frazier), where he won his second world title.
His third title came in 1978 when, at the age of 36, became the then-oldest heavyweight champion in history with his victory over Leon Spinks.
Despite his illness, in recent months he has offered his opinion on America's political stance, after Donald Trump suggested banning all Muslims from entering the US.
"Speaking as someone who has never been accused of political correctness, I believe that our political leaders should use their position to bring understanding about the religion of Islam and clarify that these misguided murderers have perverted people's views on what Islam really is," Ali declared in a statement.
The Louisville Lip was recognised by Sports Illustrated as “Sportsman of the Century” in 1999, and was voted the BBC’s “Sports Personality of the Century” in the same year.