"Eternals," the Doctor said. "Extraplanar creatures with extraordinary physical manipulation capabilities and mind-reading. They don't exist in our universe, they exist in eternity. Well, they did. They fled to the Void during the Time War and they haven't been seen since. For a while there, the Time Lords used to worship a few of them as Gods."

He sniffed and leaned his head back against the wall, reminiscing. "The White and Black Guardians are two of their most powerful. The Black Guardian tricked me into finding all of the pieces of the Key to Time once, but I figured him out, had it destroyed and scattered. He then made a pact with one of my companions to kill me. He outsmarted the Guardian, though."

Ooooh, but that was so very long ago. "I was told once that we'd have a third encounter. I wonder why we haven't."