"Birthdays of course mark the passage of time but no matter the year, one thing never changes - you are the greatest of all times," read a message by US sports analyst Bob Costas.
"A very happy birthday to you mate, the champion of all champions," wrote Australian Sandro Catanzariti.
"I still can't believe the things you have achieved in your life. You are truly an inspiration to us all."
Born Cassius Marcellus Clay in Louisville, Kentucky on January 17, 1942, Ali began boxing at eight years of age after his prized bicycle was stolen, and went on to win the light heavyweight gold medal at the 1960 Rome Olympics, completing a 100-5 amateur record.
Ali's professional record was 56-5 including 37 knockouts as he became the first boxer to claim the heavyweight title three times.
But it wasn't just what Ali did, it was how he did it.
Pride, respect and hope
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Muhammad Ali at the 1960 Rome Olympics
[EPA] |
With civil rights issues becoming prominent in the 1960s America, Ali, an outspoken, bold black man instilled pride in black culture, respect for black beauty and hope for racial equality.
After defeating Sonny Liston to claim the world heavyweight crown in Miami Beach on February 25, 1964, the great boxer announced he was converting to Islam and was changing his name from Cassius Clay to Muhammad Ali.
Ali refused to join the US Army to fight in Vietnam in 1967, and as a result was stripped of his crown and banned from boxing, keeping him out of the ring for two years at what should have been peak years in his career.
Returning to the ring in 1970, Ali suffered his first defeat the following year at the hands of Joe Frazier, before avenging the loss in 1974 ahead of his famed "Rumble in the Jungle" victory over George Foreman in Kinshasa, Zaire, as he reclaimed the heavyweight title with an eighth-round knockout.
The legend grows
In 1975, Ali stopped Frazier in the 14th round of the "Thrilla in Manila", but lost the throne to Leon Spinks in a 15-round split decision on February 15, 1978.
Ali won a 15-round unanimous decision over Spinks seven months later to again reclaim the title before retiring in 1979.
In an ill-fated comeback, Ali was stopped by Larry Holmes in the 11th round in 1980 and then climbed into the ring for the final time on December 11, 1981, at Nassau, Bahamas, losing a 10-round decision to Jamaican Trevor Berbick.
The legend grew in the years that followed, and peaked when Ali lit the cauldron at the 1996 Atlanta Olympics.
"My left hand was shaking because of Parkinson's. My right hand was shaking from fear. Somehow, between the two of them, I got the thing lit," Ali said describing the moment.
Ali, who along with wife Lonnie has moved to Arizona, will celebrate his 65th birthday privately, according to an Ali Center spokesperson.