Courtney played opposite five actors who played Doctor Who on television, reports the BBC. But he made his first appearance in 1965 on the show as a different character, Bret Vyon.
When the actor returned to the show three years later he made his first appearance as the Brigadier. He made his final appearance on "Doctor Who" in 1989, according to IMDB.com. He reprised the role on the show "The Sarah Jane Adventures" in 2008.