The God-Emperor's Inquisition
The Genestealers (Corporaptor hominis) are one bioform of the multispecies Tyranid race that was genetically designed by the Hive Mind for the infiltration of other intelligent species’ settled worlds. The genestealer subspecies and corruptions include including: Genestealer Patriarchs, the Genestealer Magus, purestrain Genestealers, Genestealer Hybrids, and Brood Brothers.
Genestealers reproduce by introducing their genetic material into a host from another intelligent species; this is normally a human, but can theoretically be any sentient humanoid race, including the Eldar or the Orks. The Genestealers have no true genders, and require a creature of any species, any gender to reproduce. The Genestealer will find a suitable host and hypnotise them into passivity using its unusual, alien eyes. The Genestealer then thrusts its long, whip-like tongue (which also serves as an ovipositor) into the body of the host, where it deposits its DNA in the form of a type of virus that infects the somatic and germ line cells of the host. Several hours later, the infected victim wakes up from the incident, with no wounds or any recollection of what happened. The new host of the Genestealer DNA will go on about its normal life, and eventually reproduce with another member of its species, thus siring (if male) or giving birth (if female) to a Genestealer Hybrid. The Genestealer reproductive cycle is truly cyclical, as an F4 hybrid will always spawn a purestrain Genestealer with a genome identical to that of the original Genestealer that infected the first host.