Xarion was a male Sith Lord of the Sith Empire alive around 3643 BBY. During the Cold War with the Galactic Republic, he began a battle with a rival Sith Lord Anathel in the Stygian Caldera nebula. Their conflict started disrupting Imperial trade, prompting a negotiator to convince them to move their battle elsewhere in the Outer Rim Territories.
He would later rise to the position of Darth and sit on the Dark Council by 3628 BBY as leader of the newly-created Galactic Influence. In this position, Darth Xarion oversaw Sith Intelligence and the former Sphere of Expansion and Diplomacy. His rival Darth Anathel would also be on the Council as Head of Sith Doctrine.
In Update 5.10 Jedi Under Siege, Darth Xarion is indirectly mentioned by NR-02 as the latter's master, who is unable to speak with the player at the time. Darth Xarion makes his first live appearance in Star Wars: The Old Republic: Onslaught as a Dark Councillor. For Republic players who are saboteurs for the Empire, Darth Xarion's identity is revealed and confers with the player over holocomm in the Slippery Slopes Cantina.
For Imperial players, after Darth Malgus is defeated on Elom, Xarion will arrive to help restrain him with the Force and arrest him.