Boxer Rocky Marciano was recognized by CBC as a world champion .
In 1983 , following the death of Kim Duk-koo from injuries sustained in a 14-round fight against Ray Mancini , the WBC took the unprecedented step of reducing the distance of its world championship bouts , from 15 rounds to 12—a move other organizations soon followed ( for boxers ' safety ) .Among those to have been recognized by the WBC as world champions were the undefeated and undisputed champion ( 46-0 ) Joe Calzaghe , Floyd Mayweather Jr ( 50-0 ) , Roy Jones , Jr. , Wilfred Benítez , Wilfredo Gómez , Julio César Chávez , Muhammad Ali , Joe Frazier , Sugar Ray Leonard , Thomas Hearns , Mike Tyson , Salvador Sánchez , Héctor Camacho , Marvin Hagler , Carlos Monzón , Rodrigo Valdez , Roberto Durán , Juan Laporte , Félix Trinidad , Edwin Rosario , Bernard Hopkins , Alexis Argüello , Nigel Benn , Lennox Lewis , Vitali Klitschko , Erik Morales , Miguel Cotto , Manny Pacquiao , Canelo Alvarez , Tony Bellew , and Mairis Briedis .