After the near-destruction of his XIXth Legion during the Drop Site Massacre on Istvaan V at the start of the Horus Heresy, Corax was desperate to rebuild his Legion. With the Emperor's permission, he and his Astartes delved deep beneath the Imperial Palace to recover the advanced genetics knowledge that the Emperor had used to create the Primarchs. Corax then made use of these techniques and a recovered original Primarch genetic template to accelerate the development of new Raven Guard Astartes. The repercussions of those actions came back to haunt him, leading Corax to eventually grant the Emperor's Peace to all the twisted, mutant spawn who emerged as the result of his experiments. Corax then vanished into the Eye of Terror in search of penance for his shame. His current whereabouts and