Disciples of the Light
The Disciples of the Light were a highly advanced civilization who, according to the Beast, lived before the universe to which the Doctor was native was created. As such, the Doctor had no knowledge of their existence and doubted the possibility of these beings.
Before the creation of the universe, the Disciples battled with the Beast, subduing it and buried it on the planet later known as Krop Tor, intending to leave it chained there for all eternity. Both the planet and the black hole, it orbited, served as a prison for the Beast. (TV: The Satan Pit) Their means of maintaining the orbit without obvious technology surpassed even the Tenth Doctor's understanding. (TV: The Impossible Planet)