"There was a goblin. Or a trickster, or a warrior. A nameless, terrible thing, soaked in the blood of a billion galaxies. The most feared being in all the cosmos. Nothing could stop it, or hold it, or reason with it - one day it would just drop out of the sky and tear down your world."
The implication is that this is one of the goodies talking about the big villain of the series, but that rather describes the Doctor himself, does it not?