A Sith Lord named Darth Nostrem, either a Human or a Sith pureblood by heritage, existed within the resurgent Empire some decades prior to the Dark Jedi Exar Kun and the Great Sith War he initiated. During Nostrem's time, two Darths, Qalar and Victun, who were members of the governing Dark Council, engaged in a particularly violent Kaggath—a Sith tradition where rivals battled each other.
This confrontation resulted in the destruction of the Imperial Citadel on Dromund Kaas, the Empire's capital planet. The Council then charged Nostrem with the Citadel's reconstruction. He was instructed to use the resources of Qalar and Victun, who had been killed by the rest of the Council, and rebuild the Citadel following the designs of the Sith Emperor. Once the structure was complete, the Emperor tested its intricate defenses by trapping Nostrem within its depths, where the Sith ultimately perished, unable to escape.
The character of Darth Nostrem was initially introduced in Star Wars: The Old Republic Encyclopedia, which served as a 2012 reference guide for the Star Wars: The Old Republic video game.