Teirna was a member of the Kazon-Nistrim and one of Seska's aides. USS Voyager answered a distress call from his shuttle in late 2372. His parents were killed in a Trabe attack shortly after his birth.
Chakotay's suspicions turned out to be correct, as Teirna was in reality a suicide bomber. He used a detonation needle embedded inside an artificial toenail and when he stuck himself with it, triggered a bomb that was embedded in his body and the explosion rendered Voyager helpless, allowing the Kazon to capture the ship. (VOY: "Basics, Part I")