Muhammad Ali, three-time world heavyweight boxing champion, was born Cassius Marcellus Clay Jr. in Louisville in 1942. At 12, he asked a local policeman for boxing instruction after his bicycle was stolen. As his enormous talent became obvious, boxing also became a means of helping his family financially.

While working his way up in the boxing world, winning Gold Gloves amateur competitions and a gold medal in the 1960 Summer Olympics, he also began studying the teachings of Islam. In 1964, he defeated Sonny Liston to capture the world heavyweight championship and, at a press conference the next morning, announced that he was taking the name Muhammad Ali on the instructions of Elijah Muhammad, head of the Nation of Islam.

Over the next several years, Ali developed a brash personal style, labeling himself “The Greatest” and boldly predicting the outcomes of his fights, down to the round in which he would knock out his opponent—and became a worldwide celebrity by backing up his boasts in the ring. Then in 1967, he received an induction notice from the U.S. Army. Ali refused to serve, citing his religious pacifism and his opposition to the war in Vietnam. He was sentenced to five years in prison for resisting the draft (though he did not serve any time), fined $10,000, stripped of his boxing title, and barred from boxing. While appealing the court ruling, he made many speeches about civil rights and racial inequality. In 1970, the U.S. Supreme Court finally voted 8-0 in his favor, and he resumed boxing.

Though Ali did eventually regain the heavyweight title, his stand had cost him several prime years of his career. In the United States, already deeply divided over both race and Vietnam, it made him a lightning rod for both admiration and resentment. In Africa, where revolutions were beginning to break the grip of colonialism, it made him a hero to millions, who saw him as a symbol of black pride and principled masculinity. Today, Muhammad Ali is a frequent choice when people pick the most influential sports figure of the 20th century—and possibly the best-known person in the world.

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