Ok can anybody explain to me what a Genestealer Cultist is?
I mean: aren't Genestealers Tyranids? Why would anyone worship them? They will come and eat everybody!?
Mostly what
@Captaniser said, but also that there are 4 main generations of Genestealer Cultists and several offshoots:
1. The first generation of Acolyte Hybrids are born from the result of the Patriarch implanting non-Tyranid lifeforms with his DNA. These are born in various ways depending on the life-form infected, but they are always the initial offspring. They have little resemblance to their host parents, just looking like a smaller Genestealer with 3 arms rather than 4 and wearing scraps of clothing.
2. The second generation of Acolytes are born from the first-generation Acolytes interbreeding with more of the native population. Again, they show little resemblance to the host race, although they resemble them more than the first-gen Acolytes, often showing more of a tendency to wear clothing.
3. The offspring of these Acolytes are the third-generation Hybrids, the first Neophytes, who have a much greater resemblance to the host race, only having a bald, ridged forehead and possibly an alien tongue or some other weird feature to identify them as a Hybrid. These are vastly different from their parents in that they are the first generation that can actively infiltrate the host race because they look so much like them - those that infiltrate humans will most often join the Imperial Guard or work in the mines or manufactora, for example, most often being so difficult to tell apart from ordinary humans that Genestealer Cults can ally with Imperial Guard (or at least they could in 6th/7th Edition). Furthermore, while the Cult is hidden it will gladly ally with the Imperial Guard stationed on the planet to combat common threats that attempt to take over the prey world, such as Chaos Space Marines, Tau and Orks.
4. The offspring of these will result in the 4th generation Hybrids. These Neophytes are almost exactly like members of the host race, the only way in which they differ from them being that they are pale in complexion and have bald heads. That’s it. These will blend further into the host race’s society even than their parents.
5. When they reproduce, the offspring are not Hybrids, but original purestrain Genestealers, thus causing the family tree to go full circle as these Genestealers will attempt to become Patriarchs of their own cults by stowing away on freighters and even warships bound for other planets belonging to the host race. A Cult’s presence on a prey world acts like a magnet to Tyranid Hive Fleets, which will immediately change course and head towards the planet when it senses the Cult’s activity. At the same time, the Patriarch will sense the Hive Fleet approaching the Cult’s planet and will lead the cult on a full-scale rebellion against the prey. The Cult will attack the Imperial Guardsmen that it previously sided with and the streets will be filled with Cultists and Acolytes who now display their Genestealer attributes. When the Tyranids arrive, they will see the Cult soldiers as other warrior-organisms and join their fight against the prey, overwhelming them from all sides. However, as soon as the last members of the prey are dead, the Tyranids and the Acolytes will turn on the Neophytes, as their job of infiltrating the prey race has now been completed, and the Neophytes will be devoured along with the comrades they deceived only a few hours earlier.
6. Aberrants are exceptional cases of Hybrids that are born with exceptional physical strength and a minuscule mental capacity. These are kept within the Cult’s HQ as bodyguards and enforcers that are used to muscle in whenever trouble breaks out in the Cult’s territory or whenever enemies come calling. They are given Power Hammers and Power Picks that they can wield with brutal ferocity and are also quite resilient because they had Feel No Pain in 6th/7th, which is basically the 40K equivalent of Regeneration without the vulnerability to Flaming Attacks.
7. Acolyte Metamorphs are Acolytes that start to grow Tyranid-like mutations when a Hive Fleet approaches the prey world, such as Lash Whips and Carnifex Crushing Claws that they can use with terrifying vigour against the forces of the prey world.
8. The Magi are special cases of Neophytes who are born with a greater intellect than their kin and powerful psychic abilities, who act as preachers among the Hybrids, dealing out sermons to their brothers that get the most to fight with renewed ferocity as well as controlling the minds of their enemies.
9. Last but not least, the Primus is a Neophyte who is born close to the time of the coming of the Tyranids whose role is that of the overall strategist and military commander of the forces of the Cult - while the Patriarch is the brawn and the charisma that incites the rebellion, the Primus is the brains of the uprising.
Hope this gives you a greater insight into the insidious Genestealer Cults...
