Besides Roy, who I'm not sure about personally, I think Tippy Larkin qualifies. The man had everything--speed, power, boxing ability, etc.--but a stiff beard.
Roy Jones Jr. gets mentioned because he got knocked out at the age of 35 for the very first time ???? WTF
Another vote for Terry Norris. That said, he took some tremendous punches, and when he was knocked out it was by some pretty hard shots. I just remember watching his (prime) career and feeling it was the one thing that hampered him. I used to watch him fight and get tagged and just hold my breath hoping that one hadn't short circuited him. Usually it didn't. When he was on, he was so great. I'll never forget the Meldrick Taylor destruction. One of the most memorial moments of the nineties for me. Guess he didn't really have a glass chin, just not a chin of granite. More like a wooden chin. Really hard wood...like solid oak. (Really nice thread)
Hearns is the best fighter to have been knocked out 3 times, having said that, Leonard wa one of the most dangerous fighters in the world at 147, Hagler was a killer of a middleweight and Barkley wa a strong middleweight too, not that for a fighter moving up from 147 despite being amazingly talented and causing a stir everytime he got hurt because of his ability.
That's not why. Once his confidence waned after Tarver KO'd him and his reflexes slowed a bit, he couldn't depend on his chin to see him through anything. He went from untouchable to KTFO in every fight right after one of the biggest wins in his career. He wasn't getting KO'd before because of his footwork and reflexes, not his chin. I don't want to hear the drained excuse because nobody's body is so weak that you are drained for life. That just doesn't happen.
Foreman was exausted v Ali who knocked a lot of fightes out and Lyle was a devastating puncher, Foreman went on to take far hardder shots than the punch Young droppe him with when he came back in the 90`s fighting wars with bangers like Stewart and Briggs who had Lewis in trouble, Lewis may have had a weaker chin than Foreman.