Chronological and political information:
Era(s):Old Republic era, Great Force War Era
Affiliation: Old Sith Empire (as Darth Diagis)
Known masters: Lord Vitiate
Known apprentices: Darth Ignatious
Lord Diagis was a mysterious sith lord during the Old Republic Era. Due to his tendency to cover his face, hands, and everything else, not much is known about his species. He was trained by Emperor Vitiate himself, and intended to replace him. He remained alive and powerless for 23930 years due to a Force-Spell from a Sha'a Na'ana.
Darth Diagis was sent on a secret mission from the old Sith Emperor, and found Inferno around 3930 BBY. Diagis slowly pushed Inferno towards the dark side, before taking Inferno as his apprentice. Together, Inferno and Diagis overtook the entire planet.
At some point, Diagis taught Inferno a ritual of Sith Magic, taught to him by the emperor, to absorb the midi-chlorians of his opponent.
Diagis and Inferno ruled Gardocia for only a few months before one remaining Sha’a Na’ana cast a Force spell on Inferno and Diagis. Inferno would remain in stasis until Diagis died, while all of Diagis' power was transfered into Inferno.
The new prince of Gardocia, which was now ruled by a more traditional monarchy, didn't know how important it was that Diagis stayed alive, and killed him.
Powers and Abilities:
Diagis presumably had great force strength, as he was trained by Vitiate himself. He also knew of the sith ritual performed by Vitiate, which left Medriaas as a shell of a world, devoid of even the force.