Alistair Gordon Lethbridge-Stewart's ancestry goes back to Scotland, according to dialogue in "Terror of the Zygons" (1975). He first encounters the Second Doctor in "The Web of Fear" (1968), when Lethbridge-Stewart is a colonel in the Scots Guards commanding a British Army detachment sent to investigate the Yeti in the London Underground. By his next appearance in "The Invasion" (1968), he had been promoted to Brigadier and was working with UNIT. When the Doctor was forcibly regenerated and exiled to Earth, Lethbridge-Stewart gave him a position as UNIT's scientific advisor after he helped defeat the Auton invasion. Other military members of UNIT included Captain Mike Yates, Sergeant Benton and Royal Navy Lieutenant Harry Sullivan.