Originally, he was a high-ranking noble of the Kabal of the Slashed Eye. Then he had the daring idea of bedding a Farseer. Due to his sheer badassery he actually pulled it off, bringing said Farseer to Commorragh. Everyone being either alarmist buzzkills who said that bringing psykers into Commorragh is bringing trouble one way or another, or jealous assholes who wanted a piece of that fine Craftworld ass (or maybe even a mix of both), they rallied behind the Archon of the Kabal of the Slashed Eye, Sathonyx's boss, and kicked Sathonyx out of the Kabal and into the pit known as Commorragh's ghetto.
Joke was on those pricks, because he managed to break out of said pit and began living as a rebel. Even though the Kabal that kicked him out put a bounty out on his head, it was full of idiots such as the incompetent dunce running it because they never managed to catch Sathonyx. This led to the Baron building up his rebel army of Hellions and other Commorragh riffraff and then aiming it at said Kabal, bringing it to his knees. What happened afterwards comes as utterly no surprise to anyone who is a Dark Eldar. Afterwards, if you're curious, Sathonyx allowed his old Kabal to remain while he remained kingpin of all Dark Eldar Hellion gangs, but the Kabal answered to him and the new archon is just a puppet with Sathonyx pulling the strings.
Oh, and if you want to hear a special detail: That Farseer he boned? She's dead. Whether or not this was the Kabal's doing was never mentioned, but it probably wouldn't have changed much. Wanna know what the Baron did about this? Turn her crystal bones into new pimp-coat accessories, which can predict the future when he drops them in a pool of blood - which is how he managed to avoid all his enemies and beat them. Damn, that's creepy; yet he's still only half as scary as Willem Dafoe.
|Dark Eldar Lords and Ladies|
| Asdrubael Vect - Archon Tahril - Baron Sathonyx |
Drazhar - Duke Sliscus - Kheradruakh
Lady Malys - Lelith Hesperax - Urien Rakarth