Earnie Shavers is the man regarded by most boxing experts as being the hardest single-punch heavyweight in history, with guys like Foreman and Joe Louis being up there as well. Shavers sneaky right hand was legendary, and he put Larry Holmes dead on his ass one night in the middle of a tremendous fight, at the time Holmes was the reigning heavyweight king. Holmes, due to his tremendous year-round conditioning and superior boxing skills, got up and won a couple rounds later.
Shavers and his people claimed that Holmes thumbed him and cried foul requesting a rematch. He never got it. The accusations made by Shavers people were also made by Scott LeDoux and his people after a game LeDoux lost to Holmes in a short fight. It is entirely possible that Holmes inadvertantly thumbed a few guys in his career, as his uppercut was one of his bread and butter punches, and depending on how it's thrown and the type of gloves being used, thumbing a guy is entirely possible.
LeDoux's protest was also denied, and being a big Holmes fan myself, these incidents, while containing some possible credibility, do nothing to take away from Holmes superiority during his six year reign over the heavyweight division. He was, because of his all around boxing skills, and tremendous attention to conditioning on a year-round basis, the best of his time.
But as for Earnie Shavers, who also hung out with some bodybuilding gym friends of mine, no one could throw a single punch as hard as he. That's what some cigars make me feel like, particularly Cubans.