Once upon a time, Fabricio Werdum was getting posterized by Junior Dos Santos by way of a vicious uppercut. Now he's set to challenge for the UFC heavyweight title. That sort of perseverance screams tough. His return fight to the UFC was against Roy Nelson, and was a battle that saw him almost finished in a standing guillotine at the end of the fight. He went on to beat Mike Russow - and Big Nog. And he didn't just beat big Nog, he submitted Big Nog. Submitting a Nogueira brother is a feat in and of itself. For all that Werdum gets to fifth on our list.