Arca Jeth — "Master Arca" in almost every panel he appears in — is an Arkanian Jedi Master with Sephi ancestry, serving as the Order's Watchman for the Onderon worlds. He runs a training compound on Arkania and taught Ulic Qel-Droma, Cay Qel-Droma, Tott Doneeta and Nomi Sunrider, which makes him the single most consequential teacher in the Old Sith Wars.
He was created by Tom Veitch for the first Tales of the Jedi arc in 1993. His death at the Jedi conclave on Deneba in 3997 BBY, killed by a dark-side attack, is the event that pushes Ulic into the plan that ruins him — a grief-driven decision by a man whose teacher told him repeatedly to keep his thoughts with the Force.
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.