Vergere is a Fosh, a former Jedi Knight who vanished on a mission to Zonama Sekot decades before the films and reappeared among the Yuuzhan Vong. She is introduced in Greg Bear's Rogue Planet (Del Rey, 2000) and becomes central to the middle of the New Jedi Order series, above all Matthew Stover's Traitor.
Traitor
Her reputation rests on Matthew Stover's Traitor (Del Rey, 2002), in which she holds Jacen Solo captive and subjects him to a programme of pain and philosophy designed to dismantle everything the Jedi taught him. The book argues, at length and seriously, that the light side and dark side are categories rather than substances. It is the most intellectually aggressive Star Wars novel ever published and it split the readership permanently.
The unresolved question
Later novels retrofitted her as a Sith who had been trained under Palpatine, which many readers regard as a flattening of a deliberately ambiguous character. Whether Vergere was a Sith, a heterodox Jedi, or something the categories do not cover is the single most durable argument on the Legends shelf, and this dossier does not settle it — her affiliation is recorded as independent because that is what the texts actually support.
What she does to Jacen
The consequences run for a decade of publishing. Everything Jacen Solo becomes in Legacy of the Force traces back to what happened to him in her custody, which makes Vergere the most consequential supporting character in post-film Legends.
Canon status
Star Wars Legends. The Yuuzhan Vong war and Vergere have no place in current canon.
