Commander Jadar was a Klingon who served the Empire's Defense Force as a starship captain, in command of Jadar's battlecruiser in the 2270s.
In the 2270s, Jadar's battlecruiser was chosen to test an experimental gravitational field weapon, a device which produced a substantial gravitational field comparable to a small quantum singularity.
After USS Enterprise was snared within the gravity field, Jadar gloated at Captain James T. Kirk, pleased to have caught the famous starship commander. Unfortunately, a blast of antimatter destroyed the weapon and heavily damaged his ship. (TOS comic: "War in Space")