Jarth, a Lumerian, was an aide to Ves Alkar, a Federation Mediator.
In 2369, Jarth accompanied Ves Alkar to Rekag-Seronia to mediate a civil war. He was unaware that Alkar was using females as "vessels" to deposit his evil and dark thoughts so that his mind could remain sharp and pure. This process killed the female vessels. (TNG: "Man of the People")
Jarth was played by Rick Scarry.