George Foreman
Evander Holyfield
Ross Puritty
Nic Valuev
Wladimir Klitschko
Vitali Klitschko
LEnnox Lewis
Samuel Peter
Ray Mercer
Shannon Briggs
Anthony Joshua

And on and on.

PRoblem is, is that most of these guys are on steroids.

I think special credit has to be given to George Foreman, as being possibly the physically strongest boxer in the pre-steroid era and in his 90's career I don't think he used them either. His 90's heavy strength training regime including weights, wood chopping and pulling jeeps on a tether was legendary.

Possibly the best image of his strength was in I think the first round of Foreman vs Morrison, where the steroid pumped, savage HW banger Tommy Morrison tried wrestling with George and with astonishing strength, big George launched the young roid head into the corner like a child.

That was strength!