Carlos Monzon
Carlos Monzon was a great fighter and a deeply troubled person. On one hand, he is known for becoming a unified WBC/WBA middleweight champion and defending this title 14 times. On the other, he is known for his violent out-of-ring lifestyle, culminating with his conviction in 1989 for murder.
In the ring, Monzon was a monster. He holds career defining victories over two other entrants on this list—Emile Griffith and Jose Napoles.