Foreman won his first 40 fights (37 by KO) before fighting Muhammad Ali. He devastated Joe Frazier and Ken Norton - two fighters who gave Ali a torrid time, both beating him on one occassion. He returned to the sport after 10 years of retirement and built his way up to winning the heavyweight championship for a second time at the age of 45.
These are just a few of the more impressive facts about Foreman, but what I want to focus on is his fight with Ali. Going in to the fight Foreman was the undisputed Heavyweight Champion after annihilating Joe Frazier and a 3-1 favourtie against Ali- whose greatness was yet to be truly secured. As we all know in the bout Ali produced a piece of tactical genius and boxing history on his way to pulling of one of the biggest upsets in boxing history. This is all well and good and adds the list of reasons arguing for why Ali is the greatest of all time, but the point I want discuss is they never had a rematch and if the did have a rematch Ali couldn't of repeated his strategy from the first fight and in my opinion in a straight fight (not the the first fight wasn't a straight fight, but you know what I mean) Foreman would have destroyed Ali.
I am also aware that at this stage in his career Ali wasn't in his prime.