Who has the best combination of elite chin and elite cardio in boxing history? Rocky Marciano comes in mind
Marciano is definitely one and to tell you the truth, I think we are seeing an ATG combination of endurance and chin with Usyk.
Hagler was the first name that popped into my head, vibranium chin and super human conditioning. Holyfield is another, Calzaghe too, Marciano another obvious choice.
A few worthy mentions already but Hagler for me,the consummate professional,never stopped and only one dubious count against him his whole career in 67 fights which replays showed was infact a slip against Juan Roldan . It’s also worth taking into account that only 3 of Haglers Championship fights were 12 rounds the rest all being 15 rounds .
Kid Gavalin. Never stopped in 143 fights and frequently went the distance. Jake LaMotta's endurance doesn't need explaining. Hagler of course is near or at the top.