Charlie Sato

Charlie Sato was a Warrant Officer who worked in the Vault.

Biography
When Charlie first became a warrant officer for the vault, he was given a tour by Captain Ruth Matheson, and in the vault they came across four objects: An army jacket, a painting, crystal and a wax cylinder, which bore a significance. Each was used in one of the Doctor's many adventures. (AUDIO: Tales from the Vault)

Sato and Matheson were later tasked with guarding the Master. This task was unsuccessful, as the Master managed to trick the duo and escaped in his TARDIS. (AUDIO: Mastermind)

Behind the scenes

 * Both Charlie and the Captain have surnames from Torchwood characters. Ruth has Rex Matheson's surname, and Charlie has Toshiko Sato's.
 * Both Yee Jee Tso and Ruth actress Daphne Ashbrook have played other characters before — Yee played Chang Lee, and Daphne Grace Holloway.