Obscure science-fiction joke

A year or two ago, the principals in my late & lamented AD&D group were sitting around idly pursuing some worldbuilding tangent or other, and we came up with the idea for this powerful undead wizard with a peculiar gap in his knowledge and memory -- he doesn't know how it was he died, or who was responsible for bringing him back as he is. Eventually, by some magical means, he travels back in time to find out, and of course it turns out that he ends up in a situation where he himself is the one who grants his corpse its fell animation.

Then he says, "I know where I came from... But where did all you non-zombies come from?"