Zannah is a human Sith Lord, the first apprentice taken under Darth Bane's Rule of Two and the first person to complete its terms. She appears as the child Rain in Dark Horse's Star Wars: Jedi vs. Sith #1 (April 2001), and is given her full life in Drew Karpyshyn's Legends novels Rule of Two (Del Rey, 2007) and Dynasty of Evil (Del Rey, 2009).
Why she matters more than her master
Bane invented the doctrine. Zannah is the test of it. A rule that says the apprentice must eventually destroy the master is only a rule if somebody actually does it, and for two novels the interesting question is not whether she is strong enough but whether she is patient enough — whether she can hold the intent for twenty years without acting on it early and without letting it curdle into ordinary resentment.
The Sith sorceress problem
Karpyshyn gives her a skill set deliberately unlike Bane's. He is a brawler who came out of a mine on Apatros; she is a sorceress whose primary weapon is Sith illusion, which lets her turn a fight into an argument with the opponent's own mind. It is the closest the Legends shelf came to writing a Sith who wins by being cleverer rather than by being angrier.
The duel on Ambria
The trilogy ends where the doctrine says it must, in a duel between the two of them, and the resolution is genuinely ambiguous about what a "victory" under the Rule of Two even means. Both Sith get most of what they wanted. Neither gets it cleanly. Zannah takes the title and takes on Darth Cognus, an Iktotchi assassin, as her own apprentice, and the chain runs on.
Canon status
Zannah is Star Wars Legends. The Rule of Two itself is canon — Yoda states the master-and-apprentice principle in The Phantom Menace, and Bane appears as a spectral vision in Star Wars: The Clone Wars — but no canon work has dramatised Zannah, and her biography, her birth name, her sorcery and the Ambria duel belong to the Legends shelf alone.
Reading note
She is the reason to read past the first Bane book. Path of Destruction is the better standalone; Rule of Two and Dynasty of Evil are where the trilogy becomes about something, and that something is her.
