The late British comic character actor, renowned for his distinctive mustache and later, balding crown, was a stalwart of the London stage, making his debut in a 1931 production of Sport of Kings. Throughout the remainder of the decade, he remained consistently employed, supplementing his acting career with a stint as a newsreel commentator for British Movietone News.
In 1938, Sumner transitioned to screen acting with ABPC Elstree, where he honed his craft and developed his signature style, specializing in the portrayal of the quintessential bumbling "silly ass." This archetype was comprised of a range of characters, including supercilious army officers and clubroom types.
One of his most memorable performances was as the utterly inept Major Upshott-Bagley in the 1958 film I Only Arsked!, which was later adapted into the popular television series The Army Game in 1957. Between 1958 and 1962, Sumner shifted his focus to writing and producing documentaries.
In 1973, he made his Broadway debut in the comedy play The Jockey Club Stakes, playing the role of Lord Coverly de Beaumont. He eventually retired from acting in 1980 and passed away nine years later on the island of Alderney.