Nightmares mindeatingbrainteria

Originally some sort of unknown, alien bacteria, Xenococcus-Cerebrax (the Neural Parasite) spread on an Empire vessel, exhibiting a strange reaction to the leaking radiation present in the ship's core. It mutated and transformed into what it is now: a hive mind of sapient bacteria. Attempting to reach out to the species who's ship birthed it, it took control of an engineer onboard it and attempted to make first contact through him. A terrible mistake. It's attempt at making contact was botched, and when it took over the engineer, it completely wiped his mind. The Empire would take no chances. The ship was blown apart by a battlecruiser sent on the guise of rescue, but fragments of the wreckage of the ship still traveled through the galaxy, and Xenococcus-Cerebrax was eventually found by a Mi-Go scouting craft, which managed to communicate with it through their extrasensory abilities. An alliance was established soon enough, with Xenococcus-Cerebrax serving a central role in the infiltration of the upper echelons of the human's command hierarchy, leaving and infecting new hosts every month, for any longer than that prompts the sudden and violent mutation of their host, either by choice of the parasite itself or by force.