physical strength, not punching power. Lennox Lewis is up there. Much as i dislike Wlad Klitschko, he was physically strong too. Holyfield (post steriods) was incredibly strong. Foreman (old version) was quite strong. Ali was very strong.
Fury. Very strong https://www.proboxing-fans.com/tyso...bject-like-a-bug-hitting-a-windscreen_070314/ https://www.thesun.co.uk/wp-content...jpg?quality=80&strip=all&w=1920&h=1080&crop=1
Shannon The (Glass) Cannon deserves a mention. I think his bench was near 500lbs. Mexican beef tacos and all.
Someone like Jack O Halloran was probably one of the strongest at his time but wasn’t good enough to be a real contender. So we only really know about the good fighters. L Lewis seems about the strongest. Foreman was strong.