Darth Sion, the Lord of Pain, was a Sith Lord who lived in the time of the Old Sith Wars. As a Sith Marauder in the Great Sith War, Sion fought for Exar Kun’s Sith Empire until the day he was struck down. Rather than die, though, Sion found that by calling on his pain, anger, and hatred, he could rise from certain death and achieve immortality, at the cost of all-consuming agony. With a body fractured and decomposing, but held together by the dark side of the Force, Sion survived the Great Sith War.

Sion allied himself with the next Sith Empire to arise in the galaxy, that of Darth Revan and Darth Malak. Those Sith, too, fell, and he watched from the Sith Academy on Korriban as the Empire tore itself apart. Sion soon found new purpose with Darth Traya and Darth Nihilus, a pair of Sith Lords who together with Sion formed the Sith Triumvirate, dedicated to restoring the Sith and eliminating the Jedi. In their headquarters on Malachor V, Sion served as Traya’s disciple. Eventually, frustrated with her teachings, he and Nihilus stripped her of the Force and cast her out. The two ruling Sith Lords went on to reunite most of the surviving Sith remnants and continue their war on the Jedi, with great success.

With the Jedi all but eliminated, Sion took notice of a new Jedi returning to known space, the Jedi Knight Meetra Surik, who had been exiled since the Mandalorian Wars. His attempt to kill her was thwarted by Traya, who managed to get Surik to Peragus II. Sion followed in a captured Republic ship, the Harbinger, but Surik and her companions escaped once more. He encountered her again at Korriban, but beginning to develop strange new feelings for her, he let her escape. Traya eventually betrayed Surik and returned to take command of the Sith and Sion. Sion awaited Surik on Malachor V; in their final battle he was struck down again and again, but rose each time. Surik showed Sion the price he paid for immortality, convincing him to let go, and the Sith Lord found peace and finally allowed himself to die.