For the regular universe counterpart, see Kesh.

In the mirror universe, Kesh was a Klingon councillor. He attempted to seize the throne from Regent Sturka, but was thwarted by Gorkon. (TOS novel: The Sorrows of Empire)

Although it was not explicitly revealed, the nature of Klingon politics suggest that Kesh was killed when Gorkon "thwarted" him.