- Division: Light middleweight, Welterweight, light-welterweight, lightweight, Super Featherweight (Champion, retired)
- Years active: 1996-2017
- Most recent profession win: Defeated Conor McGregor via TKO in 2017
It would be a mistake to leave Mayweather Jr. off this list as he will likely go down as the very best defensive boxer in the history of the sport. While not active as a pro-boxer anymore, the recipe of his last pro bout against McGregor seemed to create a new market in the sport of boxing where athletes from other sports can compete for high purses under the rules of boxing. Since he’s retired, he’s done exhibitions against MMA and kickboxing champion, Tenshin Nasukawa whom he defeated in one round, and most recently, Logan Paul in a non-scored bout, all under boxing rules. Some may be critical of his defensive style and opponents he chose, but he seems to have a knack for making casual and hardcore fans of boxing tune in.
With the number of divisions and weight classes in boxing, this list might be found lacking but losses come in all sports. In combat sports losses are lessons and some of the greatest and current champions usually taste defeat before their career ends (Mayweather excluded). In fight sports, the young eventually eat the old but carrying that “0” for a long time will always count for something.