Darth Lokess

Darth Lokess was an individual of Human or Sith pureblood descent who held the title of Dark Lord of the Sith and was a member of the reconstituted Sith Empire's ruling Dark Council during the first few centuries of the Empire's existence. During a violent storm on the Imperial capital planet Dromund Kaas, Darth Lokess summoned the other eleven Councilors to a meeting and convinced them to join her plot to destroy the Sith Emperor, though she kept an army of loyal Sith outside of the meeting in case any of the Councilors refused. The other eleven Sith Lords agreed to join Lokess' cause, but when they gathered on the steps of the Imperial Citadel in order to confront the Emperor, all eleven died instantly in a flash of light. Lokess was locked within the depths of the Citadel by the Emperor, who tortured her until her death.

Text and facts from the “Darth Lokess” article on Wookieepedia, licensed under CC BY-SA 3.0. Modified for this site.