Charlton Heston
Planet of the Apes (1968)

We'll admit to cheating a little on this one — Heston's George Taylor is not a prehistoric man, and he time-travels to the future, not the past — but isn't one man's future another ape's prehistory? Either way, even if you disagree with his place on this list, it's impossible not to be transfixed by the handsome, brooding Taylor as he attempts to save (albeit unsuccessfully) a doomed human race.