What criteria do we have to work with? Do we count debutants - or must they have had a least one pro fights?
If we include debutants, then Torpedo Billy Murphy gave 67 (if I have counted correctly) of his opponents their first defeat.
Larry Holmes handed Ray Mercer, Tim Witherspoon, Gerry Cooney, Carl "The Truth" Williams, Renaldo Snipes, Ossie Ocasio, David Bey, Marvis Frazier, Leroy Jones, Scott Frank and Kevin Isaac their first losses. Those were 11 pretty good fighters. (Isaac and Snipes floored Holmes.) Holmes also lost controversial decisions to the undefeated Brian Nielsen and the undefeated Michael Spinks (in their return fight). That stands out to me more so than an Australian featherweight from 140 years ago who reportedly knocked off 60 guys with no wins or losses on dates that can't be confirmed.
^ Yeah, it's interesting that being undefeated is worth so much in boxing, yet it's also flipped to mean "untested" and "inexperienced". Holmes was criticized for fighting many of the guys you mentioned because they were "inexperienced novices", rather than getting praise for taking on several undefeated challengers. Riddick Bowe, in his post-title comeback, fought undefeated prospects in five of his next six fights. Yet he was criticized, perhaps rightly, for taking on soft touches. While first losses can be devastating to a fighter's career and psyche, how a boxer handles the loss and whether he can come back from it really separates the men from the boys, so to speak. Muhammad Ali and Gerry Cooney are polar polar opposites in this respect. For that "0" to be worth something, a fighter has to get to a certain level and has to have turned back a stiff challenge or two. We also have to take a fighter's overall career into account. In that light, Frazier taking Ali's "0" really meant something. Holmes taking Marvis Frazier's "0" meant far less. Tyson taking Ric Spain's "0" means virtually nothing. It's all relative.
