Games Workshop's big scary monster.
Mindless Predator
The Genestealer was introduced in the original
Warhammer 40000 in the miscellaneous
scary aliens section as a
death world creature that reproduced by implanting its
eggs in unwary creatures. After the eggs were implanted, they fertilised themselves with the host's
DNA, producing a hybrid creature. By some unexplained method, the genestealers had a 'backup copy' of the original pure DNA, and if the means to implant eggs became hybridized out, could produce a new
purestrain asexually.
The purestrain resembled a
Giger alien, with a
sea anemone like ring of tentacles where the jaw would be.
Insidious Cult
When
Space Hulk was released (but still before
Alien 3), the genestealer had become much more insidious. The genestealer eggs, once implanted, were not lethal, but merely
brainwashed the host into protecting and nurturing the new hybrid. The genestealers could communicate psychicaly, and sought each other out to form a hive. Genestealer-
human hybrids became more and more intelligent with each generation, with an increasingly human appearance. From the outside, the genestealers would appear to be a secret society, or a cult, recruiting new hosts from the native population. The original genestealer, the patriarch, would control the brood, growing larger, less mobile, but with potent psychic powers. Eventually the cult would produce a
magus, a charismatic
figurehead that could pass for human under the closest scrutiny. Led by the
patriarch, the magus would take control of the the remaining uninfected hosts, and lead them to infect other cities. A genestealer infestation on a
hive world, if not spotted early, could lead to infection of hundreds of billions, and virus bombing by the
imperial navy. Typically, crack squads of
space marine terminators would attempt to root out and kill the
magus and
patriarch, giving conventional forces a fighting chance of rooting out and
killing every genestealer, hybrid and brood brother on the planet.
The genestealer now had four arms - two hands, and two large claws. The overall impression was of an armoured
velociraptor, with a deformed, humanoid head. The hybrids progessively stood straighter, had shorter tails, fewer limbs, less armour.
Manipulated Infiltrator
By the release of
warhammer 40000 version 2, it was revealed that the genestealers were merely the precursors of a much larger threat. The
Tyranids, a single huge
hive mind, travelling from one galaxy to the next, and devouring everything in their path, used the genestealers to infiltrate and
pacify entire planets, removing any resistance the planet could have posed. As the
hive fleet approached, guided by the eminations of the
patriarch, the genestealer cult came under the control of the hive mind, and the entire planet (genestealers and all) was devoured.
The general appearance of the genestealer was unchanged in this revision.