The warrior empire of the Klingons, ruled from Qo'noS, long the Federation's greatest rival and later its ally.
The Klingon Empire is the interstellar state of the Klingons, centred on their homeworld Qo'noS. Its culture celebrates honour, combat and the teachings of Kahless, the legendary warrior who united the Klingon people, and its government is led by a chancellor together with the High Council.
In the original series the empire is the Federation's main adversary, and Discovery depicts open war between the two powers in 2256 and 2257. After the explosion of the moon Praxis, the Khitomer Accords of 2293 began a lasting peace, a turning point shown in Star Trek VI: The Undiscovered Country.
By the time of The Next Generation the empire is a Federation ally and Worf serves in Starfleet. The alliance survives the Klingon Civil War and is strained in the 2370s, when Gowron briefly withdraws from the accords, but the two powers fight side by side against the Dominion.