M'tachtar

The M'tachtar were a genetically enhanced group of Klingon warriors that were created by the scientist Qadar to serve in the war against the Federation. They, along with their creator, were banished to a neutral planet for their actions. They attempted to escape by commandeering the USS Enterprise under Captain James T. Kirk but were stopped before they could overthrow the ruling leader of the Klingon Empire. They were captured and returned to Qo'nos but their fate is not known, it is likely they were executed for their attempts at a coup against the leaders of the Empire.

(Star Trek novel: My Brother's Keeper )