Sobek was a member of the Thousand Sons during the Great Crusade and Horus Heresy, a member of the Corvidae Cult and the Practicus to Chief Librarian Ahriman at the time of the Burning of Prospero. Sobek survived the purge of their homeworld, and helped Ahriman develop the Rubric on the Planet of the Sorcerers.
During the retrieval of the Iron Oculus, Sobek suffered the flesh change, but Hathor Maat put him in stasis.[2a] After returning to the Planet of the Sorcerer, Ahriman, Hathor Maat and Sanakht used their powers in a communion with the purpose of finding a future where Sobek didn't die. They found it and the flesh change seemed to stop, but then Sobek said three words: All is dust. After that, Sobek body became dust, its armour broken.[2b] That was the first step of the Rubric.