The Sith, known alternatively as Red Sith or Sith Purebloods, were a species of red-skinned humanoids that originated on the world of Korriban, before eventually resettling on the ice-world of Ziost. Also distinct for their bone spurs, facial tentacles, and genetic predispositions toward both left-handedness and the dark side of the Force, the Sith species coalesced into an empire ruled first by kings and later by Dark Lords. After the arrival of the Human Exiles on Korriban in 6900 BBY, interbreeding and genetic manipulation altered the Sith species; over the course of several generations the original species became a hybrid race of Sith and Human heritage. Original Sith blood became a symbol of pride among the Sith, with the term «Sith Pureblood» referring to Sith who had a higher than average concentration of Sith blood.
Despite a society dominated by barbarism and infighting, Sith civilization culminated in a Golden Age, after which the species was scattered across the galaxy. An eponymous dark side tradition took the species’ name, one that, despite numerous manifestations over time, maintained foundations borne of the customs, science and magic practiced by the ancient Sith species.
For the Thrawn Trilogy, Timothy Zahn initially intended the Noghri to be the Sith, but was told to change that by Lucasfilm. It is also rumored that originally the Yuuzhan Vong were intended to be exiled Sith, but that it was changed prior to the New Jedi Order series.