Trained as a Sith, Khreusis eventually reached the rank of Sith Lord. He had in his possession the mask of an ancient Sith Lord, Aloysius Kallig, and wore it with pride. He lived on Korriban in his fortress, high up in the Valley of the Dark Lords, where he was challenged by a young Sith apprentice. Originally, Khreusis thought the apprentice was there as assigned by their master, but instead, the apprentice was there to retrieve the mask of their ancestor as the latter had commanded the young Sith to. The apprentice soon thereafter revealed this fact and Khreusis threatened that he would tell Darth Thanaton about the situation. Khreusis engaged the apprentice in a duel and was easily beaten, the mask he wore finally returned to Kallig's bloodline.
Khreusis was trained as a Sith Warrior and, as such, he relied more on lightsaber combat although he still possessed some Force powers like Force lightning. But even with his skills developed, he wasn't a match for Kallig's heir.
Khreusis unmasked
Khreusis was created for Star Wars: The Old Republic, a massively multiplayer online role-playing game released by BioWare on December 20, 2011.
He appears in Lord Khreusis's Stronghold, a fortress on Korriban. Besides killing him, there is another option to gain Khreusis as an ally, which requires the use of neutral dialogue options, leading to Khreusis testing the player by ordering his two apprentices to attack. After the player wins, he gives the mask willingly, thus showing his face.