Darth Tenebrous's Sith Master

Darth Tebebrous's master was a male Twi'lek master of the Sith Lord Darth Tenebrous. During his lifetime, he imposed his teachings from the Dark side of the Force, and after years of apprenticeship, his apprentice came to realize that the Dark Side of the Force, far from being some malevolent mystic sentience bent on spreading suffering throughout the galaxy, was merely an energy source, which could be manipulated. When Tenebrous saw no further use for his master, he killed him.

The Master was also known to the Sith following him for opening a hole in the Force, allowing the Jedi to feel the dark side for the first in eight centuries.