XoXaan is one of the Dark Jedi exiled after the Hundred-Year Darkness who arrived on Korriban with Ajunta Pall and became the first Sith Lords. She appears in flashback in Dark Horse's Star Wars: Legacy and in the Lost Tribe of the Sith fiction, and her writings were among those collected into the in-universe Book of Sith.
What distinguishes her among the founders is a speciality in dark side healing — a genuinely odd corner of the mythology, since the Sith are otherwise defined by destruction. Later Legends material makes her a teacher to Darth Krayt in spirit form, which is a long reach across four thousand years. Star Wars Legends.
Catalogue entry. This figure has a verified record here rather than a full write-up — the encyclopedia labels its own depth instead of padding it.