A Daemon Primarch is one of the fallen primarchs who has been elevated to the rank of Daemon Prince by the Chaos Gods, uniting the demigod might of the Emperor's lost sons with the immortal power of the Warp. They are among the most fearsome individual beings in the galaxy, each a living god of ruin.
When half of the primarchs turned traitor during the great civil war that scarred the Imperium, the Dark Gods rewarded their most devoted with apotheosis. Angron of the World Eaters was raised as a champion of Khorne, Mortarion of the Death Guard as a favoured son of Nurgle, Magnus of the Thousand Sons as a sorcerer-lord of Tzeentch, and Fulgrim of the Emperor's Children as a chosen of Slaanesh, among others.
Unlike ordinary Daemon Princes, the Daemon Primarchs retain the vast intellect, presence, and martial genius of their original natures, magnified by daemonic gifts. From their fortresses within the Eye of Terror they brood over ancient grievances and plot the downfall of the realm their father built. When one deigns to lead a campaign into the material universe, whole sectors tremble, for few forces in existence can hope to stand against a wrathful primarch clad in the power of a god.