Cha'qi'thl
Cha'qi'thl is a Tzeentch Daemon, that the Sorcerers of the Thousand Sons' Cult of Scheming make pacts with.[1]
Those with the fortitude to band with the Daemon can bargain for a formula of great power known as Cha'qi'thl's Theorem. Many though have been driven insane trying to actualize the equations of fate the Theorems contain.[1]
Source
- 1: Psychic Awakening: Ritual of the Damned, pg. 81 - Thousand Sons: Cults of the Legions