I'd say Carlos Monzon. Unbeaten in 82 fights, and it never ended. 15-0 in fights for THE World Middleweightt Championship, a 5-0 (4) run against HOF fighters. Chavez' had an excellent run, Robinson after losing the first fight to LaMotta, Jimmy Wilde went unbeaten in his first 90-something fights.
The best has to be Willie Pep 62-0 then he loss only to then win another 28 before he had a draw and then it was another 45 wins before his next loss. His record at that time 107-1-1
Let me give you and example RinKing: JC Sr. was 68-0 before his fight against Meldrick Taylor in 1990. His next two opponents:Akwei Ado 5-3. And Russell Mosley 4-3-1. In 1991 Chavez was 77-0 and his opponent Ignacio Perdomo was 1-0. Never fought again. What would people think if Cotto, Margarito, Mosley, Williams or even Cintron go and fight some guy that has only 5 fights or less??????????? I guess it was different times.
Yep. Tyson's streak may not be as long as many other fighters but he was so dominant in those streak that at some point everybody can only wonder who can beat him. I remember clearly back in 1996, Holyfield is supposed to be just like the rest - get KOed within 3 rounds.