Career years: 1948-1956
Accolades: Career record of 49-0 with 43 wins by KO, world heavyweight champion (1952-1956)
Last stand: World Heavyweight Championship, Sept. 21, 1955: Rocky Marciano defeats Archie Moore by KO (9 rounds)

Having never lost a professional bout during his career, Rocky Marciano was one of the greatest heavyweight champions to grace the ring. He remains the only champion to hold the heavyweight title while going untied and undefeated throughout his career. The Rock from Brockton defended his title six times, lastly against Archie Moore in a bout that ended with Moore getting knocked out after nine rounds in 1955.