The Klingon Empire's intelligence agency, whose spies work under a cloud because Klingons consider covert work dishonourable, and whose agents included the surgically altered Arne Darvin.
Klingon Intelligence carries out espionage for the Empire, although Klingon culture regards spying as beneath a warrior, and an agent who fails can expect disgrace. Its best-known operative is Arne Darvin, altered to pass as human, who poisons the grain bound for Sherman's Planet in The Trouble with Tribbles and is exposed when tribbles recoil from him.
Deep Space Nine's Trials and Tribble-ations finds Darvin a century later, a ruined exile, travelling back in time to kill Kirk and redeem himself.
In Visionary three agents, Bo'rak, Atul and Morka, come to Deep Space 9 posing as stranded freighter crew to spy on a visiting Romulan delegation, hiding a surveillance device that Miles O'Brien's time shifts reveal. In Return to Grace the agency's discovery of a weapons facility on Loval prompts a Klingon raid on Cardassian space.