Rocky Marciano, was an American boxer and the heavyweight champion of the world from September 23, 1952, to April 27, 1956. Marciano is the only champion to hold the heavyweight title and go undefeated throughout his career.
George Edward Foreman (nicknamed "Big George") (born January 10, 1949) Marshall, TX Retired American professional boxer, two-time World Heavyweight Champion, Olympic gold medalist, ordained minister, author, and entrepreneur
Joe Calzaghe 46 Wins (32 knockouts, 14 decisions), 0 Losses, 0 Draws Longest-reigning world champion in recent years, having held the WBO Super Middleweight title for over ten years and made 21 successful defenses. He relinquished the title to move up to light heavyweight. As his super middleweight and light heavyweight reigns overlapped, he retired with the longest continual time as world champion of any active fighter