Sherman 'The Tank' Williams - made him do the unthinkable and quit. In all serious I think Bowe had him really hurt in their first fight round 10 and obviously KOd him in their third. He's been hurt a fair few times but is a proper warrior. I still don't know how he managed to stay up after that rocket uppercut of Bowe in their first fight (even after a little help from the ropes)
As Soloman said, don't forget Toney. Well, Bowe KOed him worse than Toney did. The other real HWs, Foreman, Lewis, Ruiz, Cooper, probably hit him much harder than Toney did too. BUT: Holyfield was competitive in all these fights, even the ones with Bowe that he lost. He was actually starting to seriously kick Bowes ass in that 3rd fight when Bowe caught him with that hook, if I remember correctly. Against Toney, from round two on, he got hit over and over again with that right hand and left hooks, while not being able to return much. By round 7 it was target practice for Toney. And Holyfield was seriously hurt when he finally went down - he got up, but had his corner not stopped it, he would have gotten stopped much worse. Toney punished and embarrassed him for many rounds - nobody has ever done that to Holyfield before, and not since either.