The 3 most "INVINCIBLE" fighters (IMO) in history all had this quality.

Sonny Liston
George Foreman
Mike Tyson

But what happened when they fought great boxers? Liston fought Ali twice and was convincingly beaten both times. But before the first fight no-one gave young Clay a cat in hells chance and people were worried for his life. That fire soon went out and the same could be said for George Foreman again he was bludgeoning people so badly that when Alis time came, again people were worried for his life but again he had a game plan and executed it to perfection and George was never held in the same regard again and ended up retiring for 10 years a bit further down the line.
Finally Mike Tyson is a slightly different story. I think that most would agree Iron Mike just had an off night against Buster Douglas for one reason or another. But we had to wait until he came out of prison before he fought a REAL quality boxer in Evander Holyfield. Now this reminded me of the Ali fights in that not many people gave Holyfied much of a chance against Tyson ( I was only 12 at the time but went for Holyfield may I add) But again the boxer came out on top with a knockout.
So from these fights it just goes to show, if you have a good boxer with a good chin they will tend to have the advantage over sheer power punchers and will probably go down in history as better fighters.
By the way I'm not trying to say that any of them 3 didn't have decent boxing skills (so don't jump down my throat with that one) they just weren't as polished as their respective opponents who were lets face it 2 of the greatest.