Muhammad Ali was a boxer.
The Cyber Boxing Zone ( CBZ ) website maintains an official list of lineal champions in professional boxing , with input from boxing historian Tracy Callis of the International Boxing Research Organization ( IBRO ) . Muhammad Ali ( [ ɑːˈliː ] born Cassius Marcellus Clay Jr. ; January 17 , 1942 -- June 3 , 2016 ) was an American professional boxer and activist . He was eventually arrested , found guilty of draft evasion charges , and stripped of his boxing titles . 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 .