Yiarhu-Kah was a member of a species designed to be ultimate killers.
He and nine others of his kind were sent to Enshu Atsukau's homeworld by the Super-Directors, charged with eradicating the population for their decadent and self-serving use of their superior psi abilities. They finished the job in a short time, leaving only a handful of survivors, including Atsukau.
A long time later, Yiarhu-Kah was sent to kill a number of witnesses in a big scandal involving the highest ranks of the Constituante. He was able to dispatch most of them and teleport their brains to the Super-Directors, but was eventually cornered by Nävis and the Unknown, who managed to lure him in a primitve trap that crushed his body. He had just enough time to realize his purpose of existence had been fulfilled, then the Unknown finished him off with his blade.