Disciples of the Light
"The Disciples of the Light", (TV: The Satan Pit [+]Loading...["The Satan Pit (TV story)"]) identified as the Disciples of Light in one source, (PROSE: Doctor Who: The Encyclopedia [+]Loading...["Doctor Who: The Encyclopedia (2007 reference book)"]) was how the Beast referred to the humanoid beings who "rose up against [him]" and imprisoned him on the planet Krop Tor. Both the planet and K37 Gem 5, the black hole it orbited, served as a prison for the Beast. The Beast's gaolers left behind a pictorial representation of his imprisonment, in a form that resembled prehistoric cave paintings on Earth. (TV: The Satan Pit [+]Loading...["The Satan Pit (TV story)"], PROSE: Doctor Who: The Encyclopedia [+]Loading...["Doctor Who: The Encyclopedia (2007 reference book)"])
Finding these wall paintings within the Beast's chamber, the Tenth Doctor gleaned a history of "some big battle… Man against Beast" which ended with the creature's imprisonment. It came to the Doctor's horror and initial disbelief when the Beast claimed that this had taken place "before Light and Time and Space and Matter. Before the Cataclysm. Before this universe was created". Indeed, the Doctor had understood that black holes were invented by his own people, the Time Lords, a claim which he maintained after seeing to the Beast's destruction. (TV: The Satan Pit [+]Loading...["The Satan Pit (TV story)"])
The diary of a time traveller claimed that the imprisonment of the Beast of Krop Tor happened on 27 October. (PROSE: Time Traveller's Diary [+]Loading...["Time Traveller's Diary (novel)"])
Behind the scenes
The script for The Satan Pit [+]Loading...["The Satan Pit (TV story)"] refers to the "Disciples of Light", which became "Disciples of the Light" when the episode was filmed. The Satan Pit establishes both that the Time Lords invented black holes, and that the Disciples imprisoned the Beast in a cosmic trap leveraging one. If the so-called pre-universe "before Time" which served as the stage for the battle is interpreted as the time before time which predated the anchoring of the thread, the possibility thus arises that the Disciples should be interpreted as the Ancient Gallifreyans. However, this is not explicit within the episode.