Chaos, also known to its servants as the Primordial Truth or the Primordial Annihilator, and to the Imperium of Man as the Archenemy, is the universal and usually malign metaphysical force embodied by the malevolent intelligent entities comprised of psychic energy that live in the Immaterium.
The entities who embody Chaos are mostly Daemons, but the term also encompasses those mortals who have thrown in their lot with Chaos, ranging from simple peasants and/or manufactorum labourers who serve as Chaos Cultists, to Traitor Imperial Guardsmen, planetary militia, Imperial nobles, planetary governors, and even the mighty Chaos Space Marines and Traitor Titan Legions of the Dark Mechanicum.
Many Astra Militarum troops have turned to Chaos over the centuries, including entire regiments of the Astra Militarum's Imperial Army predecessors that followed the Warmaster Horus into battle against the Imperium during the Horus Heresy.
These Traitors represent the primary mortal troops available to the forces of Chaos, now known as the "Traitoris Militarum" in High Gothic to the defenders of the Imperium. Even ten millennia later, Chaos Lords are known to attract these followers of Chaos into their warbands and personal armies, which vary greatly in both size and strength.
All planets and civilisations belonging to the Imperium can harbour Chaos organisations, which themselves are as diverse in practice and membership as is imaginable. From the blood-soaked sacrificial cults of feral worlds to the philosophical secret societies of more advanced worlds, the temptations of Chaos can capture all. Indeed, according to the Ordo Hereticus, Chaos Cults can arise from any class of Imperial society, be it impoverished, noble, hive-gang, abhuman, soldiers, or mutant.
A Chaos Daemon, or simply Daemon, also known as a "Neverborn" amongst the forces of Chaos, is an intelligent and usually malevolent entity of the Warp comprised of purely psychic energy. Daemons are sentient embodiments of Chaos and collectively the greatest servants of the Chaos Gods and of Chaos itself as a universal force.
Daemons are created at the whim of one of the four major Chaos Gods from a fraction of the god's own power within the Immaterium and act as an extension of its will. A Daemon's appearance and intrinsic character reflect the god's own nature. These Daemons may be reabsorbed into the god's psychic signature in the Warp at their whim.
The Death Guard are one of the Traitor Legions of Chaos Space Marines. They worship and devote themselves exclusively to the Chaos God Nurgle and as a result of his mutational "gifts" they have become Plague Marines; Astartes who are eternally rotting away within their power armour and infected with every known form of disease and decay but who are immune to all pain or minor injury.
When the XIVth Legion was first raised on Terra by the Emperor during the First Founding, its Astartes were known as the Dusk Raiders. After the XIVth Legion was reunited with its Primarch Mortarion on the world of Barbarus, he renamed the Legion the Death Guard.
The Fellgor Ravagers are Beastmen hunters, who live aboard the Gallowdark and scavenge its technology. Within the Gallowdark lurk strange cryptids and mutant tribes forgotten to the wider galaxy. Enclaves of Chaos-worshipping Beastmen dwell in barren outlands, shadowy underhives, and echoing space hulks – and even among these savage abhumans, Fellgor Ravager kill teams are the most ferocious hunters to be found. Loathed by the Imperium as a distortion of the sacred human form, Beastmen blend animal strength with embittered intelligence and razor-sharp cunning.
Corrupted by a gruesome techno-organic affiction, the Gellerpox Infected are nightmarish meldings of flesh, machinery, and
Most of these hideous beings began as loyal servants of the God Emperor.
Those origins are long gone, wiped away by supematural sickness and a compulsion to spread their infection across the Stars.
"We come from the dark, a-writhe, a-squirm, we lurch and we limp, we leer and we groan, fires fill our bellies and rot fills our brains, and fear fills the ones that we hunt in the gloom. Run, run, you shan't escape. We're coming..."
Some Traitor Marines pledged their service to all four of the Dark Gods, a malevolent force known as Chaos Undivided, whilst others preferred to dedicate themselves to the worship of only one of the Ruinous Powers. The Traitor Legions were led by the Warmaster Horus, once a primarch of the Imperium and the Emperor's most trusted friend, son, and adviser before he was corrupted by the promises and lies of the Dark Gods and his own inner flaws and ambition.
The Traitor Legions were the most powerful component of the forces of Chaos which fought during the Heresy, which also included the myriad Daemons of the Warp, Human Traitors from the Imperial Army, the potent infantry and combat walker forces of the Dark Mechanicum and Chaos Cultists drawn from across the galaxy.
The Thousand Sons are one of the Traitor Legions of Chaos Space Marines who are sworn solely to the service of Tzeentch, the Chaos God of change, intrigue and sorcery, though they were once the Imperium of Man's XVth Legion of Space Marines. The main feature that distinguishes the Thousand Sons from the other Traitor Legions is the sheer number of psyker mutations that have always existed amongst the Space Marines in this Legion.
Every current member of the Legion possesses psychic abilities and they prefer to use Chaos Sorcerers and guile in combat, relying on their psychic powers and sorcerous knowledge to earn them victory.
Chaos Space Marines, also sometimes called Traitor Marines, Renegade Marines, or Heretic Astartes, are former Space Marines of the Imperium of Man who have chosen to abandon the service of the Emperor of Mankind and dedicate themselves to Chaos to achieve their own ends.
Such corrupt Astartes usually belong to one of the nine original Traitor Legions that betrayed the Emperor during the ancient civil war called the Horus Heresy more than 10,000 standard years ago, while others come from Space Marine Chapters created long after the Heresy ended that have turned Renegade. Chaos can corrupt Astartes of any time and place just as its siren call leads many lesser men and women to their damnation.
Rubric Marines, also known by the High Gothic term Rubricae, are the spectral remnants of those Astartes of the Thousand Sons Traitor Legion who are now trapped within their suits of ancient Power Armour as mindless automatons. Remorseless, implacable foes, the Rubric Marines are forever cursed. They bestride the galaxy in armoured suits that are little more than sealed tombs, within which only a handful of dust remains of what was once a proud Space Marine. During the razing of their homeworld Prospero, the Thousand Sons Legion was forced to flee its beloved capital city of Tizca. The Emperor had sent against them the Space Wolves, the Custodian Guard and the Sisters of Silence, His intent to call the Primarch Magnus and his fellow psykers of the XV Legion to account. For all their esoteric skill, the Thousand Sons could not stand against the combined might of these invaders, and escaped to the Eye of Terror and the Planet of the Sorcerers, Sortiarius, that awaited them there through a Warp Gate opened by their Sorcerers and Magnus. However, their rapid evasion and dabbling with forbidden powers was not without price.