A Chaos Cult is the most dangerous of all those organisations that plot to overthrow the rule of the Imperium of Man from within. All planets and civilizations belonging to the Imperium can harbour Chaos-tainted 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 planets, the temptations of Chaos can capture all. The objective of the Chaos Cult is to survive and eventually dominate the society in which it dwells. Mere survival is particularly important on Imperial worlds, where Chaos worship is the greatest of heresies and Inquisitors are always vigilant and ready to wipe out any taint of Chaos.

Generally clandestine in nature, as discovery could bring with it attention from the local Adeptus Arbites contingent all the way up to the Inquisition, cults often hide behind the front of some form of legitimate Imperial organisation in their attempt to accumulate local or planetary power, such as trade unions, charitable organisations, accepted religious groups and even local variants of the Imperial Cult.

Extreme political parties make good fronts for cults, as they naturally attract power-hungry and mentally unbalanced individuals, who make particularly good material for potential cult members. A very successful organisation can achieve real political power, even gaining enough strength to make it possible for the cult to become the governing body of the planet without having to resort to outright rebellion.

After taking root, and as it expands in power and influence, eventually a Chaos Cult may end up effectively ruling anything from a township to the entire planet. Eventually, an uprising breaks out, either purposefully or because the cult has grown too large and/or unruly to remain secret any longer. At this point, the cult can be expected to summon aid from their Chaos masters, ranging from daemonic possessions of cult members to the outright summoning of members of the Traitor Legions through the Warp to the planet.

Cults may also unleash an uprising in concert with a pre-planned invasion of Chaos Space Marines. The ultimate aim of the cult's uprising is to overthrow the Imperial planetary government and attain direct control over the world. After the conflict, cultists are often taken back into the Eye of Terror where they either join the damned population of a Daemon World or are recruited (sometimes forcibly) into a Chaos Champion's armed forces or as auxiliaries to his warband.

The origins of new Chaos Cultists are legion. The teeming masses of the Imperium have colonized the galaxy from end to end. Trillions of souls labour night and day in an increasingly hostile universe. Kilometres-high hive cities boil with overpopulation, dense hab-complexes sprawl across continents, and Industrial Worlds grind and churn by the efforts of uncounted workers under the steely gaze of their high-handed overlords. But the Adepts of the established order cannot be everywhere at once.

A regime as restrictive and oppressive as the Imperium provides fertile ground for insurrection, and there are those that would foster this discontent for their own black ends. Rebellion festers in the foetid underbelly of almost every civilised Imperial world, a fire just waiting for a spark. Where the flames of heresy are given fuel, Chaos is quick to follow, turning desperate men into worshippers of the Dark Gods -- and the easy path to power and wealth they promise.

The cultists of Chaos can be found, in one form or another, almost anywhere the Imperium has spread. At first glance, they are indistinguishable from normal men and women, but under their clothes, their flesh is tattooed and branded with sigils that hurt the eyes of any faithful who look upon them. When the Heretic Astartes come to a planet, the true colours of the cultists are revealed. The powers of darkness are ever quick to promise glory, and even the lowliest initiate knows that to fight alongside such legendary transhuman warriors is to court the gaze of the gods.

Improvised armour is donned and long-hidden weapons are broken out as the cultists prepare to overthrow the Imperium one hab-block at a time. Rag-tag companies band together under the demagogues that arrive in their midst, for the everyday life of an Imperial citizen is usually so hopeless that even the hint of a new order can be intoxicating.

When open war breaks out, screaming gangs of cultists rush into battle armed with primitive solid-shot weapons, the largest of their number toting Heavy Stubbers and industrial Flamers. Despite their primitive wargear, Chaos Cultists are often able to drown a superior foe through sheer weight of numbers and a fierce desire to tear open the belly of the Imperium.

As the witch-hunting Ordo Hereticus is always keen to point out, Chaos Cultists can come from almost any background. Psychotic soldiers, cut-throat hive gangers, decadent nobles, Astra Militarum deserters, persecuted Abhumans and sewer-dwelling mutants all turn to the service of Chaos in order to improve their lot.

After all, even a man who has nothing left can still barter away his soul. The mutational "gifts" received by the most powerful cultists can be just as strange as those granted to their Chaos Space Marine masters; a favoured devotee might have muscles of living steel, flailing sucker-tentacles in place of a tongue, or the horned head of a mindless beast.

Regardless of their station, each of these dangerous malcontents trains their mind and body for the day when the favoured of the gods will lead them to a darkly glorious future, when they can rise up against the hated order of the Imperium and set the galaxy aflame.