Rocky Marciano was one of the greatest boxers of all time. He was the only heavyweight champion to retire undefeated, with a record of 49-0. Nicknamed the "Brockton Blockbuster," Marciano was known for his relentless punching power
From Wikipedia
Rocco Francis Marchegiano, better known as Rocky Marciano, was an American professional boxer who competed from 1947 to 1955. He held the world heavyweight championship from 1952 to 1956, and remains the only heavyweight champion to finish his career undefeated. His six title defenses were against Jersey Joe Walcott, Roland La Starza, Ezzard Charles (twice), Don Cockell and Archie Moore.