Putting a 4 defence minimum in there to make things interesting. I think Floyd Patterson is the only heavyweight example. Are there any similar KO machines?
After going the 15 round distance to win the WBA CW Title from Qawi by split-decision Holyfield went on to defend the title 5 times, all by KO. In those 5 defenses he also picked up the IBF and WBC belts. He even stopped Qawi in a rematch, KO4.