Parnax was a Sith Lord of either Human or Sith pureblood heritage. He lived during the time of the Sith Empire, specifically in the years preceding the Great Galactic War with the Galactic Republic. His reputation was poor, even among his relatives, and his time as a Sith was marked by constant betrayal of his allies, resulting in many influential adversaries.
Sometime around 3683 BBY, Parnax, who some perceived as either exceptionally arrogant or remarkably foolish, intentionally infiltrated the Dark Temple. This Sith structure, located on the planet Dromund Kaas, had been locked away for centuries. He sought the secret to the Sith Emperor's power. He documented his journey in multiple journals, telling of his slide into insanity as he became trapped within the Temple and uncovered the Emperor's plans to destroy all life in the galaxy. Ultimately, Parnax took his own life, convinced that he could endure the impending darkness by becoming one with the Force.
Originally, Parnax was intended to be the subject of a Codex entry within Star Wars: The Old Republic, a video game developed by BioWare. However, this entry was cut before the game's launch in 2011.