The obvious choice has been mentioned about a dozen times already, Smokin Joe Frazier. He'd walk through punches to land his own. Modern day examples are Andrade, and without being shot down and get the dksab treatment.......Derrick Chisora is fastly showing an iron chin and an iron will though it's still early and tough to tell if he will ever settle down into taking winnable fights.:think
Tyson was relentless for about 3 a 4 rounds, question was about someone who was that for all the rounds. 3 that came to my mind right away were Duran, Chavez and Pryor.
Surprised no ones mentioned Paul Williams or Katsidis yet. Apart from them the majority that came to mind have already been said. Ikbeabuchi is another one I'm surprised not to see aswell.
against absolute bums and most of them were slaps. the most fraudlent fighter of all time is more like it. his claim to fame is two 40+ year old middleweights. Hagler and Frazier come to mind. Great original thread by the way.