Born in London, Thornton had a lifelong dream of becoming an actor. Even after starting a career in insurance, he took acting classes in the evening and began starring in plays in London's West End, according to the AP. During World War II, he served in the Royal Air Force.
In the 1970s, he landed what would become his most iconic role, that of the stuffy department store manager Captain Peacock on Are You Being Served?, which ran through 1985. He subsequently starred in the series Last of the Summer Wine and appeared in movies including Gosford Park.
Thornton is survived by his wife, Beryl; daughter, Jane; and three grandchildren, the AP reports.