Kinebrach

The kinebrach were a species of simian, dog-like aliens who co-existed with the humans of the Interex. Long before humans had spread over the stars from their home world of Terra, the Kinebrach ruled a large and mighty empire. However, by the time the humans of the Interex made first contact with them, the Kinebrach empire was old and decaying. The Kinebrach, rather than choose warfare, decided to ally themselves with the forward-moving humans.

Thus, the Kinebrach were taken under the wing of the Interex, with certain limitations on placed on them. The foremost of these was than no Kinebrach was allowed to carry arms, except in times of war. Kinebrach in the Interex military took the form of shock troops due to their strong, stocky build.

Kinebrach technology, at the time of contact, was very advanced, and was one of the reason the Interex was able to progress so quickly. Their weapons, in particular, were of interest to the humans, as they had clear ties to Chaos powers. One example was a blade known as an Anathame. If the name of a target was spoken to the blade, the weapon would become totally inimical to that being, producing poisons and toxins tailored specifically to them. One of these blades was stolen by the Word Bearer, Erebus, and used through a series of events to injure Horus and turn him to Chaos.

It's safe to assume that the Kinebrach were driven to extinction when the Interex was conquered by the Imperium of Man.