The Dark King, 5th Chaos God

The Dark King is a theoretical fifth Chaos God, prophesied by both Eldar and Humans and first explicitly mentioned during the Siege of Terra in the Horus Heresy. The Dark King represents a drive for utter destruction without purpose.

Initially thought to be the Chaos-corrupted Horus or the Daemon Samus, it is later revealed that the Dark King was meant to be the Emperor of Mankind. In a desperate bid to defeat Horus, the Emperor drew immense power from the Warp, transforming into a lightning-sheathed obsidian sphere. This power inadvertently killed all nearby Custodians and terrified Daemons, the Lost and the Damned, and Traitor Space Marines.

As the Emperor began ascending into a Chaos God, believing it was necessary to save humanity, Malcador sensed his transformation and was deeply troubled. However, Ollanius Persson, John Grammaticus, Leetu, and Garviel Loken confronted the Emperor. Persson reminded Him of His humanity and persuaded Him to relinquish His newfound power, even at the risk of losing the battle. The Emperor’s decision to abandon the Dark King mantle unleashed a powerful blast that dispelled much of the Warp corruption.

Although the Emperor’s choice delayed the Dark King’s emergence, prophecy foretells that this Chaos God will eventually rise, as time is meaningless to Chaos and the Dark King’s influence already exists.