Oliver McCall: --knocked out Lennox Lewis and got the better of their series overall, losing the second fight only because he was in an unstable mental state. Despite that, Lewis' bombs couldn't phase him. --beat 6 men who had, would, or did own legitimate belts (Akinwande, Lennox Lewis, Oleg Maskaev, Bruce Seldon, Damiani, Holmes) --most bulletproof chin in history --between 88 and 2004, only lost to men who would hold claim to a legitimate title at some point in their careers, if not at the time of the fight (Douglas, Norris, Lewis, Tucker, Bruno) --viable contender in 4 decades, assuming he stays relevant.
To fight the best of your time to rematch tough fights well, Jeffries,Louis,Marciano,Ali,Lewis,Tyson,Tunney
I'm a bit surprised that no one has said Sonny Liston. He more or less laid waste to a solid group of heavyweight contenders on the way up and in the process instilled such a sense of fear in the reigning champion at the time that the heavyweight king brought a disguise to the ring when he was finally compelled to face him. He was considered to be such a force that his two losses to a young Ali were immediately dismissed by some as "fixed fights" or "dives". And in terms of head to head talent he ates very highly indeed, with many seasoned observers favoring him over virtually every heavyweight fighter who ever lived. Given that, he seems as good a choice as any to nominate.