A "boxing champion" refers to a person who is the best in the sport of boxing. They have won many fights and are considered the top boxer in their weight class. Full definition
This film tells the story of but one of the many boxing champions you've never heard of. (dvdizzy.com)
How Paul «Big Show» Wight kind of, sort of, almost — OK not really — became heavyweight boxing champion of the world (sbnation.com)
Mohammad Ali used his affirmation to become the undisputed heavyweight boxing champion of the world and arguably one of the most popular and recognized sports figures of all times! (rismedia.com)