The Man From Earth is definitely one I think about. The things he must have seen, must have done, that over time shaped him into who he was. Is he the embodiment of mankind, as well as its own self-hatred? The religious stuff was a bit much. I still haven’t seen the sequel, with genuine anxiety to.

Daybreakers is also a good one. A bit deus-ex with the “solution” at the end, but very good thought experiment