Muhammad Ali, an American professional boxer who famously proclaimed himself "The Greatest", passed away at 74.

Ali died at a Phoenix-area hospital on Friday, where he had spent the past few days being treated for respiratory complications.

Bob Gunnell, a family spokesman, told NBC News that the three-time World Heavyweight Champion boxer died this evening "after a 32-year battle with Parkinson's disease".

A funeral service is planned in his hometown of Louisville, Kentucky.

Cassius Clay to Muhammad Ali

Born Cassius Clay on January 1942 in Kentucky, he achieved fame by winning the gold medal in light-heavyweight boxing at the Rome Olympics in 1960.

By 1964, Clay was the world champion with a knockout of Sonny Liston.

In the same year, he joined the Nation of Islam and changed his name to Muhammad Ali.

Vietnam War

His career was interrupted for 3½ years in the 1960s when he refused to join the U.S. Army during the Vietnam War.

He was found guilty of refusing induction into the service in 1967, and the boxing commission revoked his license to fight.

The U.S. Supreme Court reversed that decision in 1971.

Retirement and Parkinson's

Ali retired from boxing in 1981 with a record of 56 wins, 37 by knockout, and five losses.

His diagnosis of Parkinson's came about three years after he left the ring.

Ali lit the torch to start the 1996 Atlanta Olympics, though his hands shook as a result of the disease taking further hold.

He also participated in the opening ceremony of the 2012 London Olympics, looking frail in a wheelchair.

In 2005, President George W. Bush awarded Ali the Presidential Medal of Freedom.

Ali has been married four times and has nine children.

Here are ten quotes and comments from the "The Greatest of All Time"

1. When he beat heavyweight champion Sonny Liston, he proclaimed: "I am the greatest! I am the greatest! I'm the king of the world."

2. Before his fight against George Foreman in 1974: "Champions aren't made in the gyms. Champions are made from something they have deep inside them: a desire, a dream, a vision. They have to have last-minute stamina, they have to be a little faster, they have to have the skill and the will. But the will must be stronger than the skill."

3. On his refusal to be drafted into the army: "Man, I ain’t got no quarrel with them Vietcong...No VietCong ever called me Nigger."

4. On the Vietnam War:

"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? They never called me nigger, they never lynched me, they didn't put no dogs on me, they didn't rob me of my nationality, rape and kill my mother and father. ... Shoot them for what? How can I shoot them poor people? Just take me to jail."

5. Ali described his boxing style as “float like a butterfly, sting like a bee.”

6. "Don’t count the days; make the days count."

7. "I'm so mean, I make medicine sick."

8. "If you even dream of beating me you'd better wake up and apologize.”

9. On Republican presidential candidate Donald Trump's proposal to ban Muslims from entering the United States: "We as Muslims have to stand up to those who use Islam to advance their own personal agenda".

10. When Ali was diagnosed with Parkinson's Disease:

"I'm in no pain...A slight slurring of my speech, a little tremor. Nothing critical. If I was in perfect health — if I had won my last two fights — if I had no problem, people would be afraid of me. Now they feel sorry for me. They thought I was Superman. Now they can go, 'He's human, like us. He has problems.'"

pic.twitter.com/Jr5HcJRmeA

— Muhammad Ali (@MuhammadAli) June 4, 2016

Top photo from Laila Ali Facebook

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