He won the world heavyweight championship three times, despite being banned from boxing for three years for refusing to serve in Vietnam, standing against the war long before it became a popular stance. He also repeatedly spoke out against racism and campaigned against Islamophobia following the 9/11 attacks.
Born Cassius Clay, Ali experienced racism and segregation early. He was so angry at being refused a table in a "white people's" burger restaurant in his home town of Louisville, Kentucky, in 1960 that he was reported to have thrown the Olympics medal he’d just won (as the new light-heavyweight champion) into the Ohio river.
Four years later in 1962, just after he had beaten Sonny Liston to become world heavyweight champion, he joined the radical Black civil rights movement, the Nation of Islam (NOI), and changed his name to Muhammad Ali.
“Cassius Clay is a slave name. I didn't choose it, and I didn't want it,” he said. “I am Muhammad Ali, a free name – it means beloved of God – and I insist people use it when speaking to me and of me.”
His membership of the NOI was partly prompted by a friendship with Malcolm X, the leading Black civil rights activist. They later fell out after Malcolm X clashed with Elijah Mohammad, the NOI's leader (Ali himself later left the group and converted to Sunni Islam).
Ali also publicly disagreed at first with Dr Martin Luther King Jr.’s policy of urging Black and white people to live together.
"I’m not going to get killed trying to force myself on people who don’t want me. Integration is wrong. White people don’t want it, the Muslims don’t want it,” he said.
In 1967, when Dr King spoke out against President Lyndon Johnson’s escalation of the war in Vietnam, the press asked him why he was not simply focusing on the "domestic issue" of civil rights.
He replied: "Like Muhammad Ali puts it, we are all – Black and brown and poor – victims of the same system of oppression.”
On Vietnam, Ali said:
“My conscience won't let me go shoot my brother, or some darker people – some poor hungry people in the mud – for big powerful America. They never called me n*****. I’m not going 10,000 miles from home [...] to continue the domination of white slave masters of the darker people the world over.”
Ali later made goodwill missions to Afghanistan and North Korea, delivered medical supplies to an embargoed Cuba, and even travelled to Iraq to secure the release of 15 US hostages during the first Gulf War.
He also went to South Africa to meet Nelson Mandela upon his release from prison.
Ali died in 2016.