Boxing great Muhammad Ali has passed away at the age of 74. He died at a hospital in Phoenix from respiratory issues.

Ali was perhaps the most famous person in the world during the second half of the 20th century, garnering fans and attracting controversy all over the globe. Born Cassius Clay in 1942, Ali first reached the top of the boxing world when he upset Sonny Liston in 1964 to win the world heavyweight championship. He was stripped of his title in 1967 after refusing to be drafted into service in the Vietnam War, and didn't fight for another four years.

During that time, he became a highly polarizing figure, with the country largely split over whether his actions were honorable or cowardly. Eventually, he was exonerated in a unanimous decision by the Supreme Court and regained his license to fight.

Ali faced Joe Frazier, with whom he would be forever linked, at Madison Square Garden on March 8, 1971, in what was called the "Fight of the Century." Frazier won a unanimous decision. In 1974, though, Ali won the rematch. The two would fight a third time, in the 1975 "Thrilla in Manila," with Ali winning a 15th-round TKO.

The man known as "The Greatest" won the heavyweight title for the second time when he defeated George Foreman at the "Rumble in the Jungle" in Kinshasa, Zaire, on October 30, 1974. This was a fight almost no one thought Ali had a chance to win, as Foreman had recently dominated Frazier and Ken Norton, who had also beaten Ali. Foreman said after the fight, "I'll admit it, Muhammad outthought me and outfought me."

Ali lost the title to Leon Spinks in February 1978, but then won the rematch a few months later, making him the first three-time heavyweight champion. He fought only a few more times, before retiring in 1981.

In 1984, Ali was diagnosed with Parkinson's, a condition he coped with for the rest of his life. He spent time as a sort of world diplomat, using the international fame he acquired over the previous 20 years as a way to travel the globe pursuing various causes.

Ali is survived by seven daughters and two sons.

Muhammad Ali In Training
Harry Benson/Express/Hulton Archive/Getty Images

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