Humans - Forces of Chaos: Chaos Space Marines (Traitor Legions) - The most hated enemies of the Imperium, the Heretic Astartes were once normal Space Marines, fighting together with the other Loyalist Space Marine Legions in the Emperor's name to build the Imperium in the course of the Great Crusade, but they betrayed the Emperor and turned to the service of the Ruinous Powers of Chaos during the Horus Heresy. Unlike the Loyalist Space Marines, the Chaos Space Marines work more closely with their strong network of allies such as Warp Daemons, Human Chaos Cultists and Traitoris Militarum, relying on them more often than the Loyalist Space Marines rely on the Astra Militarum. The Chaos Space Marines are still organised into the original First Founding Space Marine Legion structure, unlike the Loyalist Space Marines who were divided into 1,000-man-strong Chapters after the Horus Heresy during the Second Founding of the Space Marines. The Second Founding was spurred onwards by the adoption of the Codex Astartes, which was written by the Ultramarines Legion's primarch and the first lord commander of the Imperium, Roboute Guilliman.The Lost and the Damned - The Lost and the Damned of Chaos reside primarily, though not exclusively, within the great Warp rift in the Segmentum Obscurus called the Eye of Terror. The Lost and the Damned exist as part of a diverse and infinite collection of Chaos warbands and military hosts under the leadership of Champions of Chaos who are usually, but not always Chaos Space Marines belonging to one of the Traitor Legions. Due to the anomalous nature of time in the Warp, some of these Humans are the original Imperial citizens who sided with the Warmaster Horus during the Horus Heresy over ten thousand standard years ago, though their number has been greatly supplemented by more recent Humans who have turned to the worship of Chaos, or slaves captured as part of the many raids conducted by the forces of Chaos into Imperial space.Dark Mechanicum - The Dark Mechanicum, also sometimes referred to incorrectly as the "Dark Mechanicus," and who refer to themselves as the "New Mechanicum," is a sect of traitorous Tech-priests, members of the Collegia Titanica and Chaos Knights of the ancient Mechanicum who have become Hereteks in service to Chaos. They willingly swore their loyalty to the Warmaster Horus and the Chaos Gods as the Great Crusade came to a close and the terrible galactic conflict known as the Horus Heresy erupted in the early 31st Millennium. After the Horus Heresy ended in a pyrrhic victory for the Imperium, the traitorous forces of Chaos that had served the Warmaster were driven towards the Eye of Terror during the brutal military campaigns remembered as the Great Scouring. The Renegade Tech-priests of the so-called Dark Mechanicum were also driven from Mars by the resurgent Loyalists amongst the newborn Adeptus Mechanicus. These Renegades fled the Imperium into the far corners of the galaxy and some also took refuge in the Eye of Terror. Over the centuries, their ranks have been swelled by those Hereteks of the later Mechanicus who choose to follow their foul path into forbidden tech-heresy. In exile, the Dark Mechanicum became even more enthralled to the power of the Warp and heretical technologies.Traitor Titan Legions - The Traitor Titan Legions are those Legios of the Collegia Titanica that repudiated their oaths of loyalty to the Emperor of Mankind and willingly embraced the fickle blessing of the Chaos Gods. Driven by hatred towards the False Emperor and the Adeptus Mechanicus, these towering, warped monstrosities are now an horror to behold, possessing immense firepower that can only be matched by their Loyalist counterparts, and an insanity that allows them to happily partake in indiscriminate slaughter. They are counted a part of the Dark Mechanicum, and those Hereteks maintain these terror-inspiring war machines and offer their aid to various Chaos Lords, Chaos Sorcerers and Daemon Princes in exchange for slaves, souls, raw materiel and other services.Chaos Knights - The Chaos Knights, also known as Renegade Knights, Daemon Knights, and the Questor Traitoris in High Gothic, are Imperial Knight combat walkers, their Fallen Noble pilots and Knight houses corrupted to the service of Chaos.