Karness Muur was a Jedi Knight of the Old Republic. Seven thousand years before the Battle of Yavin, Karness Muur fought in the Hundred-Year Darkness, a civil war between Jedi Knights who served the Dark Side and those who still served the Light.
These Dark Jedi eventually lost their war, becoming exiled to the planet of Korriban. Karness and the other Dark Jedi found the indigenous species, the Sith, who could not feel the Force. Muur and the others ruled them as gods, becoming Lords of the Sith. There, Muur continued to practice his dark sorcery, where he would eventually create abominations of the dark side.