Karness Muur is one of the original Dark Jedi exiles who founded the Sith order on Korriban alongside Ajunta Pall and XoXaan. He appears in Dark Horse's Knights of the Old Republic comic and in flashback in Legacy.
His significance is an object rather than a career. The Muur Talisman — crafted by the Sith Sorzus Syn and bound to Muur's consciousness — converts those exposed to it into a controllable, contagious horde, and it keeps surfacing across the Legends timeline, most notably in the Vector crossover that ran through four Dark Horse series at once. 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.