Here are some of Ali's most memorable fights outside the ring.
Born Cassius Clay, Ali joined the Nation of Islam in 1964 and legally changed his name, first to Cassius X -- the X reflecting the unknown name he said was taken from him by slave owners centuries before -- and later to Muhammad Ali, meaning "praiseworthy one."
Many in the United States scorned Ali's name change and his alignment with the Nation of Islam, and most sportscasters initially refused to call him by his new name. When he was convicted in 1967 of violating U.S. Selective Service laws to avoid being drafted into the Vietnam War, The New York Times covered this courtroom exchange
"(U.S. Attorney Morton) Susman, who was aided in the prosecution by a Negro assistant, Carl Walker, said that he had studied the Muslim order "and it is as much political as it is religious."
Clay, who had stood stiffly in his gray silk suit and black alligator shoes without speaking, could keep quiet no longer.
"If I can say so, sir," he said, "my religion is not political in no way."
'They never called me n----r'
Ali's refusal to be inducted into the armed forces to fight in the Vietnam War on the grounds that he was a conscientious objector made him perhaps the highest-profile draft dodger in history.
"My conscience won't let me go shoot my brother, or some darker people, or some poor hungry people in the mud for big powerful America. And shoot them for what," he said
. "They never called me n----r, they never lynched me, they didn't put no dogs on me, they didn't rob me of my nationality, rape or kill my mother and father. ... How can I shoot them poor people? Just take me to jail."
Clay v. United States
As a result, Ali was convicted of refusing to report for induction. He also was stripped of his passport, fined $10,000 and denied a boxing license in every state, preventing him from fighting from March 1967 to October 1970. He spent much of his late 20s, what should have been the prime of his career, watching his case work its way through the appeals process before it reached the U.S. Supreme Court in 1971.
The court overturned Ali's conviction
in an 8-0 ruling, saying the U.S. government had failed to properly specify why Ali's application to be a conscientious objector had been denied. The decision allowed Ali to return to professional fighting.
Advocating for reporter's release from Iran
A Washington Post reporter who spent 545 days in an Iranian prison before being released in January said Ali helped his cause.
In March 2015, Ali released a statement that said, in part, "I am sorry that I cannot be physically present to lend my support in person but I pray my words will provide relief to the efforts to secure the release of Jason Rezaian. Insha'Allah. It is my great hope that the government and judiciary of Iran will end the prolonged detention of journalist Jason Rezaian."
In an exclusive interview with CNN's Jim Sciutto, Rezaian said the boxing legend is revered In Iran and when his guards heard about Ali's plea, "They started treating me in a better way. I think it brought some doubt to them about the (espionage-related) charges against me."
This was the first interview in which Rezaian has talked about his time in Iranian prison.
In a piece he wrote for his newspaper, Rezaian said of Ali's words, "It was a turning point for me. The public acknowledgment by Muhammad Ali, one of the most unifying figures in the world, that he believed I was innocent of any wrongdoing meant everything to me."
During the height of the Vietnam War, the National Security Agency tapped the phones of multiple prominent Americans, including Ali, because they criticized U.S. policy and the war.
Project MINARET intercepted electronic communications of a handful of U.S. citizens before passing them to other government law enforcement and intelligence organizations.
The ostensible goal was to monitor suspected threats to U.S. security, but the program grew to eavesdrop high-profile opponents to the war, including Ali, actress Jane Fonda and the Rev. Martin Luther King Jr.
Details of the program have gradually been made public
over the years.
Medal of Freedom recipient
Once among the foremost opponents of U.S. foreign policy, Ali in 2005 was awarded the Presidential Medal of Freedom, the nation's highest civilian award.
In bestowing the award to Ali, President George W. Bush praised
the boxer as "a fierce fighter and a man of peace."
"When you say the greatest of all time is in the room, everyone knows who you mean," Bush said. "It's quite a claim to make. But as Muhammad Ali once said, it's not bragging if you can back it up. And this man backed it up."
The award wasn't without controversy -- several members of the Veterans of Foreign Wars complained because the anti-war icon was receiving the award, ESPN reported at the time.
Taking on Trump's Muslim ban
Presumptive GOP nominee Donald Trump made headlines in December when he called for temporarily banning Muslims from entering the United States, earning the ire of Ali, perhaps still the best-known Muslim public figure in the country.
"We as Muslims have to stand up to those who use Islam to advance their own personal agenda," Ali told
NBC News in a statement. "They have alienated many from learning about Islam. True Muslims know or should know that it goes against our religion to try and force Islam on anybody."
Crusader for a cure
Ali was diagnosed with Parkinson's in the early 1980s, and quickly became an advocate for research against the degenerative brain disease. In 1997, he helped open the Muhammad Ali Parkinson Center in Phoenix to help people with the disease.
Five years later, he and actor Michael J. Fox traveled to Capitol Hill
to attend a congressional hearing to appeal for more money to support research. Ali, whose speech by then had become severely limited by his condition, was accompanied by his wife, Lonnie.
"Time is of essence," Lonnie Ali said. "People with Parkinson's don't have any time to waste. This tragic underfunding may lead to missed opportunities to better treatment or even for a cure."