Genestealers were described in an entry of the "Aliens and monsters" section of the first edition of "Warhammer 40,000" (the "WH40K - Rogue Trader" manual), but they were very different from their Space Hulk incarnation, which was more influenced by the xenomorphs depicted in the "Alien" franchise. Since the 1990s, subsequent games like "Warhammer 40,000" and "Epic" have absorbed them as part of the overall Tyranid army where they serve as the shock troops, although their origins are not related to any other Tyranid broods. A force composed purely of Genestealers can still be fielded as a sub-type of the Tyranid army, in what is known as a Genestealer Cult. The Cult is described in the in-game background as an infiltration force that weakens a target planet, infecting the local population and causing civil unrest in advance of the arrival of the main Tyranid hive fleet.