Sion along with Darth Traya and, Darth Nihilus formed the The Sith Triumvirate. Together they and their followers destroyed what was left of the Jedi after the Jedi Civil War. Sion was taught by Traya, who he would later betray with Nihilus. Traya, stripped of much of her power, would follow the Exile as Kreia.
 Powers and Abilities
Through terrible pain and eternal concentration Darth Sion learned the secrets of immortality at the Trayus Academy on Malachor V. Whenever he was struck down in battle he could call upon his anger, pain and hate to come alive again. In places strong he in the dark side he become nearly unbeatable.
He was also strongly skilled with a lightsaber.
When he was found by the Republic, the head medical officer noted that Darth Sion's bones and body appeared to have been broken potentially thousands of times in hundreds of places, and yet had been repaired each time.
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