What depicts the most terrifying encounter with alien life in fiction?

The aliens in the TV show Colony. They are nearly unseen (and that makes them all the scarier), shipping people off to slave colonies on the moon after having effortlessly taken over the planet. Their goals are unannounced and inscrutable, their power nearly infinite, and resistance against them only succeeds because they don’t care enough to do anything about it — until they do.

And their henchmen (and women) are other humans, part of the Vichy-style world government that they control. And the really terrifying part is that they seem to believe they are helping humanity.