Ruth Matheson

Ruth Matheson was a UNIT commissioned officer, with the rank of Captain, who for a time, was placed in charge of the Vault, an archive where many of the alien artifacts found on Earth were housed during the 20th century.

Biography
Matheson gave Charlie Sato a tour of the Vault when first became its warrant officer. 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)

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

After the escape of the Master, Matheson, along with Sato, was relieved of her duties at the Vault and 'reassigned', having been deemed a Category-One Security Risk due to the risk of the Master placing any post-hypnotic suggestions inside her mind. Relocated to a private residence for compromised UNIT personnel, Ruth believed that any tampering made by the Master would wear off in time, and so kept herself busy by completing several degrees, unlike Sato who felt that his career, and life, were now over. However, they earned a chance at a reprieve when they were recruited back into action by Mike Yates, who needed their help to investigate what had happened to the Vault during a communications blackout and subsequent loss of contact with several investigative teams. Although it was mostly expected by the higher ups that the assignment would be a 'suicide mission', both Matheson and Sato were able to survive, and Yates promised to make sure that their security status would be reevaluated and they would return to active duty. (AUDIO: The Screaming Skull)