I haven't seen a man tougher then Ali in the ring. I can be critical of him on a lot of things but honestly, his chin is the zenith in boxing. Jeff Fenech would fight a panzer tank. Sung Kil Moon was as close to having a riot shield for a face as you could get. Emile Griffith may not be someone you think of straight away but besides the Carter fluke he was as sturdy as they came and had a drink your blood attuited when he was pushed. Fighting Harada was a monster, Manny Pac deserves to be mentioned he was made of old boots I remember Kostya Tszyu's fight with Vince Phillips and I was shocked how many rights Tszyu ate and how much dog he had in him going out on his shield. Prince Naz carried on like a sore loser and got gritty when it wasn't going his way but he left his chin out there for flush shots and ate them all up till the end against Barrera. You won't find many if any fighters at the highest level who aren't willing to out gut you.
Tough, tough guy. But If memory serves the "grin" had something to do with him being a mouth breather because he had issues with his nose.
Archie Moore no doubt. Road warrior willing to fight ATGs at the drop of a hat and was willing to die for it in the ring.