Thanks to a reader for pointing me to Russell E. Saltzman's essay "Reel Aliens" at First Things, an on-line religion journal. Saltzman says he's greatly looking forward to the remake of The Day the Earth Stood Still (I have to admit I'm not!). Soon to be admitted to the large body of unnecessary Hollywood remakes, this new film will take a nearly perfect sf classic and transform it into environmentalist schlock starring (*shudder*) Keanu Reeves. Keanu Reeves!! I can just hear the painful dialogue now: "Like, Klaatu barada, uh, nikto...dudes." This guy single-handedly ruins movies he's in. He managed to ruin Much Ado About Nothing, for crying out loud. He makes Shakespeare sound bad!
All that aside, Saltzman's essay gives a brief look at messianic extraterrestrial figures from movies (he inexplicably leaves out the recent Superman Returns, but he's not exactly aiming for an exhaustive list anyway).
It's been a while since I've seen the original Day the Earth Stood Still, but I think Saltzman gets the plot wrong. As he describes it, Klaatu comes to Earth to destroy it right away, but changes his mind. As I remember it, it was Klaatu's plan from the start to warn Earth to stop its violence, lest it be destroyed. Maybe someone else remembers better than I do.