Dnyarri
The Dnyarri were an extremely ancient and evil race who could control the minds of others. Their discovery by a young Ur-Quan scout led to the quick collapse of the Sentient Milieu, to the thousands of years of Ur-Quan slavery and their race´s eventual splitting in to the Kzer-Za and the Kohr-Ah.
The Dnyarri favored the Ur-Quan over the other species of the Mileiu, due to their weak resistance to mind control. They used the Ur-Quan to wipe out many member races of the Mileiu over time. During this period, the Dnyarri re-engineered the Ur-Quan DNA into two types, the green (Kzer-Za) who were the political leaders and scientists, and the black (Kohr-Ah) who were the builders, warriors, and general "do"ers.
The Ur-Quan leaders Kzer-Za and Kohr-Ah learned to resist mind-control through continuous self-torture, and used their freedom to broadcast the message to the rest of the Ur-Quan, who similarly inflicted pain and agony upon themselves to relinquish their minds from the Dnyarri control. The freed Ur-Quan slaughtered the Dnyarri en masse.
Death wasn't a good enough punishment for the Dnyarri in the eyes of the Ur-Quan. As they had been engineered, so too did the Ur-Quan re-engineer the Dnyarri into sub-sentience, making eternal slaves of them, using them to communicate for them whenever they communicated with a species they felt was less advanced than they were (which was often). These Talking-pets are used aboard all Dreadnought and Marauder vessels.
The Arilou recently found a Talking Pet in the wreckage of a Dreadnought at Alpha Pavonis VII. They took it to the Umgah at Beta Orionis to heal it back to health.
The Arilou describe the Dnyarri as the most evil race known to this galaxy.