Darth Kahn

Varis Kahn a.k.a Darth Kahn was a Sith Lord that was allied with Revan during the Jedi Civil War. Through the use of the Dark Side of the Force he managed to gain enough power for immortality and survived all the way through the Old Republic era. He kept a low profile during most other eras returning during the Rise of the Empire era and the Rebellion era.