Tsao was a member of Starfleet and a crewmember of the USS Rutledge in the 24th century. In the 2360s, Tsao was a member of the away team that beamed down to Setlik III to rescue the colonists from the Cardassians. Captain Maxwell ordered Tsao, along with Volodzhe and Meier, to cover one of the street blocks when they transported down. (DS9 novelization: Emissary)