Kruge was a Klingon captain active during the latter half of the 23rd century. Commanding a Bird of Prey, he was eager to amass power and believed he could do so by gaining control of the Genesis Device. After acquiring classified data related to the device, he visited the Genesis planet itself in the hopes of capturing key Genesis personnel, accidentally destroying the USS Grissom in the process but managing to capture the away team on the planet's surface.
Following the arrival of the damaged and undercrewed Enterprise, Kruge killed David Marcus and threatened to do the same to Saavik unless Kirk surrendered his ship. After Kirk destroyed the Enterprise, denying Kruge his prize and killing his boarding party, the two captains fought on the disintegrating Genesis planet. Kirk finally killed Kruge by kicking him into a lava stream.