Freedon Nadd is a human Jedi student who fell to the dark side, trained under Naga Sadow, killed him, and made himself king of Onderon. He appears in Dark Horse's Tales of the Jedi from 1993, in the arc Ulic Qel-Droma and the Beast Wars of Onderon.
A villain who is already dead
The structural trick is that Nadd's story happens four centuries before the comics are set. What the Jedi encounter is his sarcophagus, his holocrons, and a royal line that has been quietly serving his instructions for generations. He is the Legends shelf's first proper demonstration of the idea that a Sith Lord's real weapon is the material he leaves lying around.
The Freedon Nadd Uprising
Dark Horse gave the aftermath its own arc in 1994. The Jedi try to dispose of the artefacts; the cult that has grown up around them fights back; and the attempt to clean up Onderon is what draws Ulic Qel-Droma and Exar Kun into everything that follows. Nadd is the fuse for the entire Great Sith War.
Teacher of the dead
His spirit tutors both Kun and Ulic at different points, which makes him the connective tissue between the two ancient Sith empires the comics built — Sadow's, and the one Kun assembles two thousand years later.
Canon status
Star Wars Legends. Nadd and Onderon's Sith history are not part of current canon, although Onderon itself appears in The Clone Wars.
