Aetaos'rau'keres, the Slayer of Souls, is a Lord of Change, a Greater Daemon of Tzeentch. He is known by many other names and falsehoods across the galaxy, including: the Lord of Hosts, Distorter of Worlds, The Shadow of All Colours and None, Ashenwing, Render of Veils, and Tzeentch's Mad Satrap.
The true origins of the being known to some as Aetaos'rau'keres has been lost even to the scholars of the arcane in the Imperium, though the Blue Scribes chatter that this daemon lord has hunted down and extinguished every mortal soul or Warp entity that knows the truth of his nature save for his patron lord Tzeentch. Aetaos'rau'keres is a dreaded and feared figure amongst the pantheon of Tzeentch, his name spoken in hushed tones and shrouded ambiguities even by those who worship the Great Conspirator.
The extreme power and mastery of the Warp that this loathsome creature possesses allows him to pierce the veil of time and turn the power of other psykers against themselves. Though the daemon lord has been granted great power, Tzeentch has fettered his servant in multiple layers of ward-pacts and riddling incantations, controlling this Lord of Change's ultimate fate. These restrictions on his free will and the determination of his own fate have shattered the Greater Daemon's reason, making him spite-filled and hateful.
When he is summoned forth upon the mortal plane, the daemon is forced to appear and vent his wrath. Only the most apocalyptic of Tzeentchian cults would venerate such a hateful creature, seeking to bring forth this daemon lord only when their intent is to murder whole worlds in the name of Tzeentch.
- Imperial Armour - Apocalypse II, pp. 62-63