Ambassador Treen was a Kradin diplomat in the 2370s. In 2374, the crew of the USS Voyager contacted Treen to enlist his people's assistance after crew member Chakotay was captured by the Kradins' enemies, the Vori.
After Chakotay's successful rescue from the Vori, Treen attempted to express his relief at his safe return. Unfortunately during his imprisonment by the Vori, Chakotay had been subjected to an extensive brainwashing scenario designed to make subjects hate the Kradin. Accordingly, he was not receptive the Ambassador's friendly overtures, even after learning the truth. (VOY: "Nemesis")