Genestealer

Tyranid bioform created to infiltrate enemy planets. They arrive by boarding space hulks or voidships, and infecting the local population so that the offspring of the infected consists only of genestealer hybrids. There are four generations of hybrids, each more humanlike than the previous one, that work togheter to destabilise the planet's society and leave them ripe for devouring by the fleets by creating cults. Cults are made up of hybrids and brainwashed humans alike, and are led by the first genestealer to arrive, the Patriarch. Said Patriarch is a psyker, and powerful one, that can lead every member of the cult in stead of the Hive Mind itself. It also acts as a psychic beacon for the Hive Mind, leading it to the planet, probably without the Patriarch knowing.

The genestealers were first encountered on the moon of Ymgarl.