Some really big mean got into the sport in the 1800s, because it attracted people who would have had other options today, such as being professional strongman competitors. There were some relatively obscure fighters, who were said to have performed incredible feats of strength.
Young George Foreman ko's any of the giants mentioned...and about as easily as he did the previously mentioned illegitimite son of Albert Anastasia.
Hes got the mean mug of his Pappy but that's about it but he played a hell of a criminal against Superman
Haakan Brock was a big I think Swedish fighter who made a few headlines because of his sheer size and also scored a devastating KO over a fighter called Charles dread which sadly made the news highlights for the wrong reasons . Brock was a very limited heavyweight and made no real impact during his career You said big but they didn't have to be good