Disciples of the Light
The Disciples of (the) Light were a highly advanced civilization which lived in the previous universe.
Appearance
Pictograms made by the Disciples of Light show them as black, humanoid creatures with white heads. How much of that is simply artistic design is unknown, although many Earth cultures drew similar stick figures with black 'Stick figure' bodies and white heads. (DW: The Satan Pit)
History
Before this universe, the Disciples encountered a species of Demon and they fought a war against each other. When they came into this universe, they fought in Mutter's Spiral, however the Demons ended up outnumbered and imprisoned by the Disciples and became imprisoned in various places including simple prisons under time rifts (such as where Abaddon was buried, under the Cardiff rift) and in complex traps around black holes (such as where The Beast was buried, in Krop Tor orbiting K37J5).
After the Beast was sealed away, the Disciples of Light seemed to have disappeared, leaving only shards of pottery and the Notebook. Translations are nearly impossible, since the language (and the alphabet) seems to have no modern decendants.