Diocletian Coros

Diocletian Coros was a Tribune of the Adeptus Custodes, formerly Prefect of the Hykanatoi, who served the Emperor during the Siege of Terra. He is placed on Terra and in the Imperial Palace, and his career belongs to the Horus Heresy rather than to the ten thousand years that followed it. He is recorded as having served earlier in the Hetaeron, before rising to the prefecture of the Hykanatoi, the Custodian formation that carries out the Emperor’s more covert and personal commissions. He became Tribune after Ra Endymion vanished, taking over the direction of the Custodes’ efforts at a time when the Emperor’s attention was largely turned to the Webway.

As Tribune, Coros organised the next wave of Custodes sent into the Webway, and he fought at the portal alongside Ra and the Emperor. He escaped that engagement and afterwards received the visions that Ra had been given. This binds him to the Emperor’s Webway project beneath the Palace, which the Siege of Terra later made the most contested ground in the Imperium. When Horus’s forces arrived, Coros held the Inner Palace and the Eternity Gate together with Sanguinius, the Primarch of the Blood Angels, in the phase of the Siege that preceded the fall of the outer defences.

He then took part in the boarding of the Vengeful Spirit, Horus’s flagship, where he and Constantin Valdor, Captain-General of the Custodes, were scattered. Brought down in the course of the fighting, Coros nevertheless reached Lupercal’s Court in time to see what Horus had left of the Emperor. He triggered the teleport that returned the Emperor’s body to the Palace. Accounts of the boarding treat the scattering of Custodes and Primarchs as a general feature of the action, so his movements there are best read alongside those of Valdor and the Emperor’s other companions.

Coros’s later fate is not recorded in the surviving Custodes tradition beyond the Heresy, and the site therefore lists him as dead. The Ten Thousand, as the Custodes are also known, remember him as a tribune who sought a good death and was instead assigned to carry the Emperor’s body home. His significance in the wider chronology rests on that final act: he stands between the Emperor’s wounding aboard the Vengeful Spirit and the Custodes’ long vigil over the Golden Throne. On the Orrery map his anchor is Terra, and on the timeline his hooks are the Webway portal action before the Siege and the Siege of Terra itself. His nearest neighbours are Ra Endymion, Constantin Valdor, Sanguinius and the Emperor.