The assistant to Nilz Baris who is revealed as a surgically altered Klingon agent when the tribbles react to him, and who later returns seeking revenge.
Arne Darvin serves as the assistant to Federation official Nilz Baris on Deep Space Station K-7. In The Trouble with Tribbles he appears to be an ordinary, if nervous, human bureaucrat helping to protect the station's quadrotriticale grain for Sherman's Planet.
When the grain is found poisoned with a virus, and the tribbles that ate it are dying, Kirk notices that the creatures react with hostility to Darvin, as they do to Klingons. McCoy's examination confirms that Darvin is a Klingon agent altered to look human, and he is arrested for the sabotage.
Darvin returns in the Deep Space Nine episode Trials and Tribble-ations. Disgraced by his failure, he travels back in time aboard a captured ship in a plan to kill Kirk with a tribble bomb, and is thwarted by Benjamin Sisko's crew. He was played by Charlie Brill in both appearances.