Ambassador Treen was a Kradin delegatet in the 2370s. In 2374, the crew of the USS Voyager contacted Treen to enlist his people's assistance after Commander Chakotay was captured by the Kradins' enemies, the Vori. Treen beamed aboard the Voyager with two assistants to negotiate with Captain Kathryn Janeway.
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")