Ezzard Charles
Rocky Marciano won the heavyweight title in 1952 and held the title until his retirement in 1956. In his boxing career he had 49 fights, all of which he won with 43 won by knockout. The only person to go 15 rounds with Rocky Marciano was Ezzard Charles in a title fight in 1954, which Marciano won by a unanimous decision. The two fought again later that same year and Marciano knocked out Charles in the 8th round.
