Tan Tsu was a male Human engineer in the 24th century United Federation of Planets. In 2367, he served aboard the Federation freighter Arcos. During its final mission, the ship was destroyed by a warp core breach. Tan Tsu and the ship's pilot escaped in an escape pod, and landed on the planet Turkana IV. They were captured by one of the two factions who controlled the planet, the Alliance. The Alliance demanded weapons in return for their release. When the USS Enterprise-D came to retrieve them, Tan Tsu was directed to communicate that he would be killed if their demands were not met.