George Chuvalo was a Heavyweight boxer with a ton of fights when Heavyweight boxing had some serious killers, and he was never KO'd. He only lost to prime George Foreman by corner stoppage and Joe Frazier by cut stoppage. He also had 2 decision losses to Muhammed Ali and a decision loss to Floyd Patterson. Not only did the guy never show signs of his chin cracking, he has his wits about him pretty good as an old man. Who would you say MMA's closest equivalent to Chuvalo would be? For a while, guys like Big Nog and Hendo had never lost via strikes, but their careers lasted long enough to see them get stopped relatively easly.