Clay won the gold medal at the 1960 Summer Olympics in Rome for light heavyweight boxing, despite almost not competing on the U.S. team due to his fear of flying.

Clay made his debut as a professional boxer on Oct. 29, 1960 and earned the nickname "Louisville Lip" for both his verbal taunts and distinctive style.

Clay became the heavyweight champion of the world on Feb. 25, 1964, after defeating reigning champion Sonny Liston. It was at this match that Clay coined the iconic phrase “float like a butterfly, sting like a bee.”

The day after the match, Clay confirmed in a press conference that he had converted after joining the Nation of Islam. He renounced his last name and called himself Cassius X until March 6, 1964, when Elijah Muhammad of the Nation of Islam gave him his official holy name, Muhammad Ali.

Ali refused to fight in the Vietnam War for religious reasons -- a decision that led to the New York State Athletic Commission suspending his boxing license and revoking his heavyweight belt. He was also arrested for draft evasion, but the Supreme Court eventually overturned his conviction on June 28, 1971.

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Coined as the “Fight of the Century,” Ali fought against defending heavyweight champion Joe Frazier -- who had received Ali's title after it was stripped from him -- on March 8, 1971. The fight was Ali’s first defeat as a pro boxer, as he was knocked out after 15 rounds.

The 32-year-old later defeated 25-year-old champion George Foreman in 1974 in a bout dubbed “The Rumble in the Jungle,” regaining the Heavyweight Champion of the World title that was taken from him.

Despite losing the heavyweight championship title to Leon Spinks in February 1978, Ali regained the title seven months later, making him the first boxer to win the heavyweight champion title three times.

The champion boxer officially retired at 39 years old after losing a match to Trevor Berbick in 1981. He was later diagnosed with Parkinson’s in 1984.

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Ali was inducted into the International Boxing Hall of Fame in 1990.

In 2005, President George W. Bush presented Ali with the Presidential Medal of Freedom, the highest civilian award in the nation.

The boxer and philanthropist opened the $60 million Muhammad Ali Center in Louisville, Kentucky, in 2005. The cultural center, which focuses on social responsibility, also serves as a museum dedicated to Ali's career.