British company Games Workshop and their publishing platform, Black Library, have constructed two events, the Horus Heresy and the Dark Imperium, in their gaming and novel lines that create two distinctly Arthurian figures who rely on the literary history of the Arthurian cycle. The Emperor and his son, Roboute Guilliman, have emerged as Arthurian candidates in these narratives. The Emperor unites planets under one banner, forges the knight-like Legiones Astartes, and then, ultimately, leaves the battlefield in favor of passive rule. The end comes when he leaves his son in charge of guarding and solidifying his power. In an Arthurian twist, the Emperor and his traitorous son, Horus, meet in battle: Horus is slain by the Emperor, but the Emperor is fatally wounded, and is entombed in the Golden Throne, a machine that keeps the Emperor alive even as his body decays. While no Avalon, the Emperor’s “death” is drawn straight from Arthurian analogues. Guilliman, foster-son of King Konnor, was the unifying force of the Five Hundred Worlds of Ultramar. Guilliman carried on his foster-father’s legacy, ruling justly and trusted by those under his rule. Guilliman’s true parentage is revealed, and from there the Arthurian elements only escalate. After the Emperor’s “death,” Guilliman keeps the Imperium together through codified laws and leadership. His own “death” comes at the hand of a traitorous brother, but Guilliman is put into stasis to heal, and amongst his followers it is said that Guilliman will return to lead the Imperium in its darkest days. Guilliman does return, and creates new Space Marines, consolidates the Imperium, and wields his father’s blazing, Excalibur-like sword. I argue that the literary history upon which these two characters rely is vital to the understanding of the world of Warhammer 40,000 and its own mirrored history of our literature.