Black, Muslim and proud, Muhammed Ali won the heavyweight title three times and became a voice for black and white American youth. His father, Clay Senior, was a sign painter, while his mother, Odessa Grady Clay, was a household domestic.
Robbed of his bike in school, Cassius Clay started to box at 12. As a high school student, he won the national Golden Gloves middleweight championship in 1959 and 1960, and the AAU national light heavyweight title in 1960, then the light heavyweight gold medal at the Olympics. He had his first professional fight on 29 October, 1960.
For his sixth professional fight against Lamar Clark in 1961, Clay composed a ditty predicting how and when he would beat his opponent. His prediction was correct, knocking Lamar out in the 2nd round. The rhymes became part of his persona.
The clear outsider, Clay challenged and beat Sonny Liston on 25 February, 1964. Misreading Clay's exuberance as nervousness, Liston was typically over-confident and was unprepared for any result other than a quick knockout victory. Clay went on to take the fight after Liston failed to answer the bell for the seventh round. Clay won the rematch the following year with a first-round knock-out.
Now the undisputed heavyweight champion of the world, Clay revealed that he was a member of the Nation of Islam and that he had been given the name Cassius X, discarding his surname as a symbol of his ancestors' enslavement.
Shortly after, Malcolm X - a black Muslim minister - took Clay on a guided tour of the United Nations building. He announced that Clay would be granted his 'X'. That same night, the leader of the Nation of Islam, Elijah Muhammad, issued a statement that Clay would be renamed Muhammad (one who is worthy of praise) Ali (fourth rightly guided caliph). Only a few journalists accepted it at that time.
As a supporter of the radical Nation of Islam, Ali spoke against the assimilation of black and white races, maintaining that black people should remain culturally distinct.
In 1967, Ali caused further sensation, by refusing to fight in Vietnam. He claimed his religious beliefs prevented him and famously blurted out to reporters, "I ain't got no quarrel with the Viet cong", becoming a hero to young conscientious objectors.
He was arrested, had his boxing license suspended, and was stripped of the heavyweight title. He was unable to box for two years while the case went to appeal.
At the trial, the jury, after only 21 minutes of deliberation, found Ali guilty. The judge imposed the maximum sentence. After the decision was upheld at an appeal hearing, the case went to the U.S. Supreme Court. During this time, people turned against the war and support for Ali grew.
In 1970, Ali was once again allowed to fight again. On 28 June, 1971 in Clay v. United States, the Supreme Court reversed his conviction with a unanimous decision.
Ali was granted a license to box in Georgia because it was the only state without a boxing commission. In October 1970, he defeated Jerry Quarry. Shortly after this the New York State Supreme Court ruled that Ali had been unjustly denied a boxing license.
In December that year, he fought and beat Oscar Bonavena at Madison Square Garden having been granted permission to fight again in New York. This paved the way for a title bout against the unbeaten Joe Frazier.
Ali and Frazier met the following year for a fight that became known as '"The Fight of the Century."
The fight was one of the most eagerly anticipated bouts of all time and remains one of the most famous. Frazier retained the title on a unanimous decision, dealing Ali his first professional loss.
In 1973, after a campaign to force a rematch with Frazier, Ali split two bouts with Ken Norton before beating Frazier (who had lost the title to George Foreman) on points in their 1974 rematch, to earn another title shot.
In the infamous 1974 'Rumble in the Jungle', he slaughtered the supposedly invincible Foreman. The fight was held in Kinsasha, Zaire, and Ali employed the now famous Rope-A-Dope to tire Foreman out, before flooring him in the eighth round.
Ali won the title again in 1979 and finally retired in 1981 with a career record of 56 wins (37 by knockout) and five losses.
Unfortunately, the boxing legend was diagnosed with Parkinson's disease in 1984. This neurological condition attacks the part of the brain that controls the body's movements.
In 1986, Ali married his fourth wife, Yolanda 'Lonnie' Ali. They had known each other since Ali was 22. They have one adopted son, Asaad. Ali also has seven daughters and one other son.
Despite his condition, Ali has remained a public figure. In 1985 he served as the referee of the inaugural WrestleMania event, held by the World Wrestling Federation.
He was also involved in a number of high profile activities to personify the vitality of the US Constitution and Bill of Rights in the late 1980s, including riding on a float at the Tournament of Roses Parade to commemorate the 200th anniversary of the Constitution in 1988.
Ali published an oral history called 'Muhammad Ali: His Life And Times' by Thomas Hauser in 1991. The same year he travelled to Iraq to negotiate the release of American hostages with Saddam Hussein. In 2002, he travelled to Afghanistan as a UN Messenger of Peace.
He has won numerous honours since his diagnosis including a Spirit of America Award for being the most recognised American and the BBC's Sports Personality of the Century in 1999. Ali received more votes than the other four contenders put together.
Ali was also named the 'Kentucky Athlete of the Century' later the same year. In 2005, he was presented with the Presidential Citizens Medal by President George W Bush.
On 19 November 2005, he set up the $60 million not-for-profit Muhammad Ali Centre as this was his 19th wedding anniversary.
As well as displaying his boxing memorabilia, the centre focuses on peace, social responsibility, respect and growth.
In 2001, a biographical film called 'Ali' was released. It was directed by Michael Mann and starred Will Smith as the boxer. The film received mainly positive reviews with Smith revealing that he only took the part after Ali told him to, declaring:
"Man, you're almost pretty enough to play me."