The Klingon Diplomatic Corps (KDC) was a branch within the Klingon Empire.
The KDC was a major component of the Imperial Contacts Branch and was charged with diplomatic missions. The organization's mission covered a very thin objective that involved bringing worlds under Klingon control through non-militaristic means. This included peaceful negotiations, assisting a party in power, terrorist operations, weapon sales and so on. Through such means, a dissident group could potentially enter into power in their government which became indebted to the Klingons who ensured that they remained in power. This made the Empire so entrenched within the assisted government that they could not exist without the Klingons continued aid. Should the group turn against the Empire, then the Klingons simply propelled a new powerful group into power. The KDC also set up incidents that were used as an excuse for Imperial intervention.
It was estimated that roughly 90% of their activities were done behind the scenes. The remaining 10% was done by real diplomats that carried out actual diplomatic missions. (FASA RPG module: The Klingons)