British-born Hickson, who trained at the Royal Academy of Dramatic Art, played Delia in the Ayckbourn comedy, earning a Tony as Best Actress in a Featured Role. Among her countless stage credits are Peter Nichols' A Day in the Death of Joe Egg (she played Grace) at the Brooks Atkinson Theatre on Broadway in 1968, and Nichols' The Freeway in London in the 1974-75 season. She appeared in about 100 movies.
She is best known, however, for the role she earned at age 78: Agatha Christie's pesky, matronly sleuth, Miss Marple, in the popular BBC series seen widely in the U.S. on the A&E cable channel. Her mannish looks and arched eyebrows in the series made her an indelible presence. She played the role until she was 90.
Her husband, Eric Butler, a doctor, predeceased her in 1967, according to the Associated Press. She is survived by two children. The cause of her death was not announced, the AP reported.