He proclaimed himself the greatest of all time.

Very few people disagreed with him through the years.

Muhammad Ali, the only man in the history of boxing to win the undisputed heavyweight championship three times, died surrounded by family at Scottsdale Osborn Medical Center after a long battle with Parkinson's disease.

"After a 32-year battle with Parkinson’s disease, Muhammad Ali has passed away at the age of 74," family spokesman Bob Gunnell told reporters. "The three-time World Heavyweight Champion boxer died this evening.”

Ali became one of the most dynamic personalities in American sports history. He won a gold medal in the 1960 Olympics, and then shocked the world with a 7th round TKO over Sonny Liston when he was just 22 years old. Ali was considered such an underdog that Liston never took the young boxer seriously, hardly training for the fight because he was so convinced he would win.

Ali proved the first bout was not a fluke with a decisive first round knockout of Liston in the rematch.

Ali lost three years in the middle of his prime because of his opposition to the Vietnam War. Ali refused to join the armed forces and fight based on his religious beliefs after joining the Nation of Islam. Convicted of draft evasion, he was later cleared when the Supreme Court unanimously overturned the conviction in 1971.

It was that same year Ali lost his first professional fight to Joe Frazier in a 15-round unanimous decision. Ali had to wait two years before a shot at the unanimous heavyweight title again when he knocked out George Foreman in the 8th round of the famous "Rumble in the Jungle."

Ali retired with a 53-5 record, losing 3 of his last 4 fights, all fought after Ali had turned 36 years old.

Ali in later life became focused on issues such as peace, social responsibility, respect, and personal growth. He made those the foundations for the Muhammad Ali Center in Louisville, Kentucky, his hometown.

Ali's battle with Parkinson's Disease began in 1984, three years after his retirement from the sport. Many family members and those close to the champion believe the blows to the head suffered through his decades of boxing contributed to the onset and development of the disease.

"Muhammad Ali was not only a great boxer inside the ring, but he was such an icon for the civil rights movement outside the ring. He’s simply, the Greatest," wrote former boxing champion Sugar Ray Leonard.

Ali wrote in his 2013 autobiography how he would like to be remembered:

"I would like to be remembered as a man who won the heavyweight title three times, who was humorous, and who treated everyone right. As a man who never looked down on those who looked up to him, and who helped as many people as he could. As a man who stood up for his beliefs no matter what. As a man who tried to unite all humankind through faith and love. And if all that’s too much, then I guess I’d settle for being remembered only as a great boxer who became a leader and a champion of his people. And I wouldn’t even mind if folks forgot how pretty I was."

Tributes poured in from around the world after Ali's passing at 74.

Legendary boxing promoter Bob Arum said in a statement: "A true great has left us. Muhammad Ali transformed this country and impacted the world with his spirit. His legacy will be part of our history for all time."

Many celebrities shared their thoughts on Twitter:

"God came for his champion. So long great one." - former champion Mike Tyson

"Rest in peace, Muhammad Ali. The true People's Champion. " - Britain's Prince Charles

“We lost a giant today. Boxing benefitted from Muhammad Ali’s talents but not nearly as much as mankind benefitted from his humanity.” - boxer Manny Pacquiao

"RIP Muhammad Ali...we will miss your spirit and humanity. You were shunned,excoriated and jailed for the same reason that made you a hero..." - former tennis star Martina Navratilova

"My heart is deeply saddened yet both appreciative and relieved that the greatest is now resting in the greatest place. May God bless the family and all of us that are left behind that were deeply touched by his life. There will never ever be another one like him." - former boxer Roy Jones, Jr.

"Let us celebrate his life. This is not a time to mourn. This is a time to try to emanate the job he was doing and the burden he leaves behind for us to carry on, to remember that the people are the most important." - legendary boxing promoter Don King

"Until Ali no one said 'I'm beautiful' he was royalty, yet common man was his pal. That is beauty. Greatest kind." - former champion George Foreman