Sam Langford.
The guy knocked out 128 opponents and carried his power all the way from lightweight to heavyweight.
How dangerous a puncher was he? Let's put it this way: In order to secure fights, he would have to agree at times to take it easy on his opponents. Nobody really wanted to step into the ring with him, including Jack Dempsey who openly admitted to being afraid of Langford. He wasn't very big, which made his deadly power all the more shocking.