Klaa is one of the two secondary antagonists (along with Sybok) of Star Trek V: The Final Frontier. In that film he was a young Klingon starship captain who strongly desired to make a name for himself. He later had a minor role in the next film, Star Trek VI: The Undiscovered Country.
Klaa is first shown destroying the Pioneer 10 probe with his Klingon Bird-of-Prey, while lamenting that the lack of an actual war between the Klingons and the United Federation of Planets meant that he could not fight a worthy opponent. Shortly thereafter, he received a signal from the Klingon High Command, ordering him to rescue their ambassador General Koord, who had been taken prisoner by Sybok, from the planet Nimbus III. Klaa had other ideas however, and realized that because Nimbus III was in neutral space, he would be able to legitimately attack whoever the Federation sent to rescue their own ambassador. He became even more determined to do this when he discovered that this person was James T. Kirk, now an infamous figure in the Klingon Empire due to Project Genesis and his killing of Commander Kruge and most of his crew.
The Bird-of-Prey took somewhat longer to arrive at Nimbus III than the USS Enterprise-A, but had a tactical advantage with its cloaking device and the Enterprise suffering severe system malfunctions. By the time Klaa arrived Kirk and his landing party had already been captured by Sybok, who forced him to take him and his followers up to the Enterprise by shuttle. Klaa realized Kirk was on the shuttle and prepared to destroy it, but Kirk had the shuttle deliberately crash-landed in the Enterprise shuttlebay, allowing the ship to escape.
Later, Klaa's second-in-command Vixis intercepted a distress call from Kirk, revealing that their destination was the planet Sha-Ka-Ree at the center of the galaxy. Klaa ordered his crew to pursue the Enterprise, despite their protestations about the dangers of the Great Barrier surrounding Sha-Ka-Ree. The Barrier proved no threat however, and Klaa caught the crew of the Enterprise unawares, crippling the ship. Klaa demanded that Kirk be handed over to him, but Spock had Koord relieve Klaa, whose attack had never been authorized by the Klingon High Command, of his duties.
Star Trek VI: The Undiscovered Country
Klaa was next seen in a minor role as the court translator for Kirk and McCoy during their trial at the hands of General Chang, presumably having been demoted to this position for his actions in the previous film. Despite his history with the two defendants, he seemingly carried out his duties efficiently and correctly.
Klaa is one of only a few named villains in a Star Trek film to survive the events of the film. The other villains include Maltz from the third film, Admiral Cartwright and Valeris from the sixth, and the alternate reality Khan Noonien Singh in Star Trek: Into Darkness (the Borg Queen was destroyed on-screen in the events of Star Trek: First Contact, but her subsequent appearances on Star Trek: Voyager confirmed that her consciousness survived the destruction of her bodies).
Though the sixth film does not explicitly name Klaa as being the translator during the trial sequence, subsequent novels confirm that it was indeed him, and that he had been demoted to this lowly position as a result of Chancellor Gorkon weeding out overly aggressive starship captains to aid his peace talks with the Federation.