Foreman before Ali Tyson before Tokio Douglas The Bodybuilder before Ruiz Wlad before Fury Liston before Ali Holmes before Spinks Ali before Frazier Hagler before Leonard Lewis before Rahman Jones before Tarver
From this list, I would say Liston, Foreman, Tyson, Wlad, Joe Louis and Jack Dempsey. The rest, while there's all time great fighters there, you could never say they looked unbeatable.
You have some good names there! I think I'll stick with my expanded list, starting with Sullivan. They all had their windows when they looked unbeatable by many at the time, IMHO, of course.
Of the names I picked from your list, I can say with absolute certainty Liston, Foreman and Tyson. They were monstrous looking invincibles. Wlad looked pretty perfect early on but not in their league, Loius is before my time, in the age of Dempsey black fighters were discriminated against. Holyfield was my fav but he was a warrior who had to dig deep, Larry Holmes had a lot of close shaves, great champion but not invincible in my view. Either way, nice post.