Ali has to be up there with 4 (Patterson, Frazier, Foreman, Spinks) but I think someone beat 5. Tito Trinidad beat 3 (Oscar, Pernell and David Reid).
Mike Tyson (Michael Spinks, Tyrell Biggs, Henry Tillman) Evander Holyfield (Henry Tillman, Ray Mercer, George Foreman) Wladimir Klitschko (Ray Mercer, Alexander Povetkin) Vasyl Lomachenko (Guillermo Rigondeaux, Luke Campbell)
Felix Savon prevented Ibragimov from winning one, so Wlad could have three if not for that (or possibly if Savon went pro).
I remember an old thread from boxing zcene where a guy was doing this trivia and Ali wasn't the answer. I can't find it anymore but I remember looking it up and it was correct, can't remember the boxer tho.
Floyd was in Rome for the 1960 Olympics. Ali with his outgoing personality was like the mayor there. When Ali told Floyd what he was going to do in his own inimitable way Floyd thought he was crazy. If you like to read you should read David Maraniss's book on the 1960 Olympics.
Biggs was just about to make a comeback and outbox Mike Tyson. It was set to be a great come from behind win, but the powers that be wanted Tyson to stay in power, so they threatened the referee to stop the fight.