Joe Frazier
He gets brutalized by George Foreman, beats Ali once and gives him a heck of a fight every other time they fought, and Ali pretty much punks Foreman easier than he ever beat Frazier.
So how does that work? Why could Ali beat the heck out of Foreman, winning by KO, yet had trouble stopping Frazier's advances?
Why wasn't Frazier able to stand against Foreman's punches, yet could take Ali's all night even though he KO'd foreman with those same punches?