A tharavul.
The practice of tharavul was a Klingon act of barbarism against the Vulcan civilization.
History and specifics[]
Vulcans would be taken into the Klingon Empire and lobotomized, with the telepathy sections of their brain removed. With mental growth stunted, the tharavul Vulcans lost their advanced mind rules, becoming little more than humanoid computers. In the early 23rd century, tharavul were enslaved by wealthy Klingon masters for varieties of menial tasks.
A tharavul named Sudok officiated a klin zha match played between Kethas epetai-Khemara and Mabli vestai-Galann. (TOS - Worlds Apart novel: The Final Reflection)