Tan Tsu was a Human who served aboard the Federation freighter Arcos.

After the ship was destroyed by a warp core breach, Tan Tsu and a fellow companion 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 Turkana IV Alliance. They demanded weapons in return for their release. Tan Tsu appeared on the view screen and informed the USS Enterprise -D that he would be killed if the demands were not met.

The other faction, the Coalition, offered to help Captain Picard rescue them, but this was a ruse to disable the Alliance's defense grid. Tan Tsu and his companion were rescued by an away team from the Enterprise-D. (TNG: "Legacy")