Muhammad Ali was a boxer.
The Fight of the Century ( also known as The Fight ) is the title boxing writers and historians have given to the boxing match between WBC/WBA heavyweight champion Joe Frazier ( 26 -- 0 , 23 KOs ) and Ring magazine/lineal heavyweight champion Muhammad Ali . Cassius Clay was born and raised in Louisville , Kentucky , and began training as an amateur boxer when he was 12 years old . Ali is regarded as one of the leading heavyweight boxers of the 20th century . In professional boxing , the undisputed champion of a weight class is a boxer who is recognized as the world champion at that class by each boxing organization .