Treen is the Kradin ambassador in Nemesis who works with Voyager to find the missing Chakotay, revealing that the Vori have been conditioning the commander to hate and kill the ambassador's people.
Ambassador Treen is a Kradin diplomat who appears in the fourth-season Voyager episode Nemesis.
When Chakotay's shuttle is shot down over a planet at war, Voyager turns to the Kradin for help. Treen comes aboard and explains that their enemies, the Vori, seize outsiders and train them as soldiers. The audience has meanwhile seen the conflict only through Chakotay's eyes, in which the Kradin are monstrous beasts and the Vori are gentle victims.
Tuvok, working with Kradin forces, finds Chakotay inside a Vori simulation built to indoctrinate recruits. Back on the ship Treen thanks the crew for their co-operation, but Chakotay cannot look at him without revulsion and admits that hatred is harder to stop than to start.