The remarks and actions were even more controversial than the former Cassius Clay’s conversion to Islam in 1964. The Vietnam War was popular at the time in the U.S., and the sight of a man, especially a black man, who not only refused to serve—but did so eloquently—incensed the sporting, media, and political establishments. Ali instantly became a national pariah—perhaps the most hated man in the country, as can be evinced in this monologue from David Susskind, the American television host, who was addressing Ali: (The link itself is worth following for Susskind’s obvious antipathy toward the man on the television screen.)

I find nothing amusing or interesting or tolerable about this man. He’s a disgrace to his country, his race, and what he laughingly describes as his profession. He is a convicted felon in the United States. He has been found guilty. He is out on bail. He will inevitably go to prison, as well he should. He is a simplistic fool and a pawn.

Nor was Susskind the only man, nor whites alone in opposing Ali’s actions: Jackie Robinson, the first black man to play in the major leagues, said Ali’s stand was hurting African Americans who were, unlike him, fighting in Vietnam.

“He’s hurting, I think, the morale of a lot of young Negro soldiers over in Vietnam,” Robinson said. “And the tragedy to me is, Cassius has made millions of dollars off of the American public, and now he’s not willing to show his appreciation to a country that’s giving him, in my view, a fantastic opportunity.”

Ali, though, didn’t see it that way: “I would like to say to those of the press and those of the people who think that I lost so much by not taking this step, I would like to say that I did not lose a thing up until this very moment, I haven’t lost one thing,” he said. “I have gained a lot. Number one, I have gained a peace of mind. I have gained a peace of heart.”

Still, Ali’s continued refusal to go to Vietnam—despite repeated pressure—coincided with the war’s growing unpopularity in the U.S. And in the three years he didn’t fight, Ali became a prominent speaker at college campuses across the U.S., as the anti-war movement grew in strength, silencing those who told him to participate with his compelling arguments:

Eventually, state boxing commissions did grant Ali licenses to fight. And when he returned to the ring, on October 26, 1970, he knocked out Jerry Quarry in the third round. The road to legal exoneration took longer. My colleague Matt Ford explains what happened:

When Ali appealed his case to the U.S. Supreme Court for the final time in 1971, liberal stalwart Justice William Brennan convinced his colleagues to hear the case. Justice Thurgood Marshall recused himself because he had been solicitor general when Ali was prosecuted. That left eight justices, who on a first vote sided with the Justice Department in a 5-3 decision. Ali claimed he qualified for conscientious-objector status because he opposed the war as a black Muslim. The Justice Department challenged that status, citing his statements that he would fight the Vietcong in a “holy war” if they fought Muslims. The justices began drafting their opinions when one of Justice John Marshall Harlan II’s clerks convinced him to take home Elijah Muhammad’s Message to the Blackman in America. Harlan returned to the Court the next day and, convinced of Ali’s sincerity after reading the text, switched sides. Harlan’s move raised the prospect of a 4-4 split, which would preserve Ali’s conviction and send him to jail without explaining why. The justices instead chose to resolve it on narrow technical grounds and unanimously vacated the conviction.

Ali triumphed, but his victory came at great personal cost. As Angelo Dundee, his trainer, said Ali’s beliefs cost him “the best years of his life.” Before he was prevented from fighting, “it seemed impossible to hit him,” he said. The man who returned to the ring “was more flat-footed.”