Thaum Rystra was a Dark Jedi who served the Galactic Empire during the Galactic Civil War. He later became a member of the Rebel Alliance, but eventually abandoned the Alliance to become the apprentice of the Sith Force ghost Valik Kodank.
While Rystra was a child, the Galactic Empire discovered him and his Force-sensitivity. He was taken from his home, and he was trained to serve the Galactic Empire as a Dark Side Adept. When the Empire sent him to kill his parents, Rystra murdered them and subsequently realized what a monster he had become, so he abandoned the Empire and joined the Rebel Alliance.
Rystra later became the apprentice of the spirit of the Sith consort Valik Kodank and wanted to resurrect her to a physical form. He believed that he could achieve this by using the Force energy of Caeleb, a Force-sensitive child who had been referred to in an ancient prophecy as the "Child of Light." Rystra also eventually found a Force-sensitive Whiphid, Tol Skaros, who worked as an enforcer for the Hutts. Thaum sensed how strong Skaros was in the Force and offered to take the Whiphid as his apprentice. Skaros agreed, and Thaum trained him to use the dark side of the Force. After training Tol as a Dark Jedi, Rystra prepared to send his apprentice on dangerous assignments to hunt and fight other Force-users, known as Jedi. Skaros refused to learn how to use a lightsaber like most Dark Jedi; instead he would buy various weapons to fight the Force users.
Rystra sent his apprentice to the world Dalicron-4 to capture Caeleb. He found out that Caeleb's parents were skilled in the Force and believed that the assignment would give Skaros some useful combat experience.