Freedon Nadd was a Jedi Padawan of the Old Republic who fell to the dark side after he was passed up for promotion to Jedi Knight. He later became the new apprentice of the exiled Sith Lord Naga Sadow on Yavin 4. After killing Sadow and conquering Onderon, He became the Royal king of Iziz but was killed after losing Onderon. Nadd's spirit then became the master of Exar Kun. After training Kun in the ways of the Sith, Kun betrayed Nadd and destroyed Nadd's spirit.
He is featured in the Tales of the Jedi series. And also mentioned in Star Wars Knights of the Old Republic II: The Sith Lords, as well as the player's character getting to visit Nadd's tomb in the game.