Heavyweight - Muhammad Ali
Cruiserweight - Evander Holyfield
Light Heavyweight - Archie Moore
Supper Middleweight - Joe Calzaghe
Middleweight - Marvin Hagler
Junior Middleweight - Thomas Hearns
Welterweight - Sugar Ray Robinson
Junior Welterweight - Julio Cesar Chavez
Lightweight - Roberto Duran
Junior Lightweight - Alexis Arguello
Featherweight - Willie Pep
Junior Featherweight - Wilfredo Gomez
Bantamweight - Carlos Zarate
Junior Bantamweight - Khaosai Galaxy
Flyweight - Jimmy Wilde
Junior Flyweight - Michael Carbajal
Minimumweight - Ricardo Lopez

Other fighters that I wanted to include in the list:

Joe Louis
Ezzard Charles
Carlos Monzon
Harry Greb
Henry Armstrong
Sugar Ray Leonard
Aaron Pryor
Miguel Canto
Eder Jofre