Be it in the sense of long accomplished careers or the ability to absorb punishment and get through tough fights, who comes to mind?
Me and Lach spoke about this fairly recently, actually. I had it similar to this, in no particular order. James J Braddock Maxie Rosenbloom Joey Maxim Gene Tunney Saad Muhammad HMs Eddie Mustafa Muhammad Glen Johnson
He was, but he was also dropped a lot, it is hard to see other LHWs going 15 with Marciano but a lot of what made Charles work so well in the Marciano fight was his Pristine positioning and defence. I'd wager his chin was on a similar level to Qawi, EMM or Tarver. He's probably an HM. Obviously just imo.
First name I thought of. Few fighters could take on the level of fighter that he did and so often and immediately back into the fray after a win or loss.