Yates' guard

Yates' guard worked at the Global Chemicals, where he was ordered by Jocelyn Stevens to keep Mike Yates under observation.

Biography
The guard was tricked into allowing Yates to speak briefly with the Third Doctor, who was disguised as one of the regular cleaners, Doris Griffiths, when Yates said he left his briefcase in his office and went to get it. He and Stevens eventually found Yates in his office. When they left, the guard asked "Doris" how her husband was, not knowing it was the Doctor. (TV: The Green Death)

Behind the scenes

 * The on-screen credit for Brian Justice incorrectly reads "Yate's Guard", instead of the grammatically correct "Yates' Guard" which appears in Radio Times.