Klaa

Klaa was a young 23rd century Klingon starship commander on a personal mission to make a name for himself in the Klingon Empire. With the assistance of his first officer, Vixis, Klaa pursued any challenge he could find.

A worthy prey
In 2287, his Bird-of-Prey encountered the ancient Earth space probe, Pioneer 10, which was found for use as target practice. Klaa destroyed the probe, but admitted that, "shooting space garbage is no test of a warrior's mettle." He thirsted for a target that would fight back.

After receiving a priority message from Qo'noS, Klaa learned of a situation on Nimbus III where the Klingon consul, General Korrd, had been taken hostage; along with the Terran and Romulan consuls. Klaa reasoned that the Federation would be sending a rescue ship of its own, so he set course for Nimbus III seeing this as an opportunity to engage a Federation ship.

En route, Klaa intercepted a Starfleet message confirming a Federation rescue ship was dispatched to Nimbus III, the starship USS Enterprise (NCC-1701-A). Klaa recognized the ship as belonging to Captain Kirk, further driving his desire to engage Starfleet. Klaa believed that if he could defeat Kirk, he would be the greatest warrior in the galaxy.

Klaa later arrived at Nimbus III shortly after the Enterprise. As his ship approached the planet, Klaa made the intentions to attack clear, by approaching the system with his cruiser's cloaking device engaged and its weapons fully charged.

Unknown to Klaa, Kirk was not aboard the target Enterprise, and was actually aboard the nearby shuttlecraft . Klaa quickly altered his attack course to target the shuttle, however, he was unable to do so in time to strike. The shuttle landed in the Enterprise hangar deck and the Federation starship went to warp. Klaa quickly attempted to establish a target lock on the Enterprise and fired on her, but missed the shot as the starship quickly warped away. Despite his initial defeat, Klaa admired Kirk's ingenious escape.

Following the Enterprise's escape, Klaa would later intercept a distress call from the vessel, which was now under the control of the Galactic Army of Light. Klaa used this to his advantage, as Vixis replied, impersonating a member of Starfleet Command. Through this ploy, they were able to ascertain the exact location of the Enterprise, allowing Klaa to follow it as it traveled towards the galactic core. Disregarding the threat of crossing the Great Barrier, Klaa vowed to hunt Kirk down, no matter where it took him.

The Great Barrier
Upon breaching the Great Barrier and reaching the galactic core, Klaa was finally able to successfully attack and disable the Enterprise. Klaa presented the terms that any attempts to raise shields or arm weapons would result in their destruction, and that the only reason they were alive was because he wanted the renegade Kirk. Handing him over would spare the Enterprise. Fortunately for the Enterprise, General Korrd was aboard. Korrd ordered Klaa to stand down, and relieved him of his command.

Klaa's ship then descended on to destroy the malevolent being on the planet, and ultimately to rescue Kirk. At the bequest of Korrd, Klaa apologized for his attack on the Enterprise, noting that this was not authorized by the Klingon government. Klaa and his crew were later invited to a reception aboard the Enterprise, where he saluted Kirk for being a worthy foe. 

Background information
Klaa was played by actor Todd Bryant.

and the state that Bryant's Klingon translator role was a reprisal of Klaa.

The Klingon Academy PC game mentions that Klaa was demoted for his unauthorized actions during the events of Star Trek V, hence his appearance as a lowly court translator in Star Trek VI. The text in the game's manual also suggested that Klaa may one day command a ship again, implying that he was making progress in redeeming himself.