Genestealer Cults

A Genestealer Cult begins when a Genestealer plants its seed in a human host. The victim becomes a Brood Brother, bound to the brood's psychic will, and the offspring of the implanted are Hybrids, part alien and part human. Over generations the Cult spreads through a world's society, its most human members infiltrating the government and defence forces. The Patriarch, the first and oldest Genestealer, holds the brood together; the near-human Magus speaks and acts on its behalf. The brood emits a psychic signal that draws a Tyranid hive fleet, and when the fleet nears, the Cult rises in revolt.