Mainwaring was born in 1885 to Edmund Mainwaring and is a pompous, blustering figure with an overdeveloped sense of his importance, fuelled by his social status in Walmington-on-Sea as the bank manager and his status as Captain and commander of the local Home Guard volunteer unit. He became commander of his home guard unit by saying that he had served as a captain in the last British conflict, despite serving 'somewhere in the Orkneys' during the Great War and only being deployed to France in 1919, the year after the armistice was signed. He was later officially designated as the Captain by the GHQ, in the episode "Room at the Bottom", after his brief reduction in rank. Despite his claim to be the son of a master tailor, it is revealed that his father was a poor draper and a heavy drinker, as is his profligate brother, Barry, who is a travelling salesman specialising in novelty toys. He has many redeeming qualities: he is essentially brave, loyal and industrious, generally kind-hearted beneath the bluster and unfailingly patriotic.