The Klingons were a humanoid warrior species that originated from the planet Qo'noS in Star Trek. One of the major powers of the galaxy, the Klingons were a proud, tradition-bound people who valued honor and combat. The aggressive Klingon culture had made them an interstellar military power to be respected and feared.
Kahless the Unforgettable founded the Klingon Empire some time in the 9th century through the performance of many heroic feats. He unified the Klingon people when he killed the tyrant Molor. Kahless came to be revered in Klingon society to the point of near-deification.
The Klingons' relationship with Humans and the Federation was rocky at best. By 2223, relations between the Federation and the Klingon Empire degenerated to a point of relentless hostility, which lasted for several decades. Later, another conflict erupted into what was considered the Federation-Klingon War of 2267.
Like their Human, Cardassian, Vulcan, and Romulan counterparts, Klingons and many of the Milky Way's species all shared a common ancestry back to the Ancient Humanoids and the DNA code they produced and seeded across the galaxy. Though each evolved under separate conditions from each other, their shared DNA allowed these species to remain roughly compatible and viable with each other.