Agatha Christie
Hercule Poirot and Miss Marple

Christie's first published book, The Mysterious Affair at Styles, was released in 1920 and introduced the detective Hercule Poirot, who appeared in 33 of her novels and more than 50 short stories.

Over the years, Christie grew tired of Poirot, much as Doyle did with Sherlock Holmes. By the end of the 1930s, Christie wrote in her diary that she was finding Poirot "insufferable", and by the 1960s she felt he was "an egocentric creep". Thompson believes Christie's occasional antipathy to her creation is overstated, and points out that "in later life she sought to protect him against misrepresentation as powerfully as if he were her own flesh and blood". Unlike Doyle, she resisted the temptation to kill her detective off while he was still popular. She married off Poirot's " Watson ", Captain Arthur Hastings, in an attempt to trim her cast commitments.

Miss Jane Marple was introduced in a series of short stories that began publication in December 1927 and were subsequently collected under the title The Thirteen Problems. Marple was a genteel, elderly spinster who solved crimes using analogies to English village life. Christie said, "Miss Marple was not in any way a picture of my grandmother; she was far more fussy and spinsterish than my grandmother ever was", but her autobiography establishes a firm connection between the fictional character and Christie's step-grandmother Margaret Miller ("Auntie-Grannie") and her "Ealing cronies". Both Marple and Miller "always expected the worst of everyone and everything, and were, with almost frightening accuracy, usually proved right". Marple appeared in 12 novels and 20 stories.

During the Second World War, Christie wrote two novels, Curtain and Sleeping Murder, featuring Hercule Poirot and Miss Marple, respectively. Both books were sealed in a bank vault, and she made over the copyrights by deed of gift to her daughter and her husband to provide each with a kind of insurance policy. Christie had a heart attack and a serious fall in 1974, after which she was unable to write. Her daughter authorised the publication of Curtain in 1975, and Sleeping Murder was published posthumously in 1976. These publications followed the success of the 1974 film version of Murder on the Orient Express.

Shortly before the publication of Curtain, Poirot became the first fictional character to have an obituary in The New York Times, which was printed on page one on 6 August 1975.

Christie never wrote a novel or short story featuring both Poirot and Miss Marple. In a recording discovered and released in 2008, Christie revealed the reason for this: "Hercule Poirot, a complete egoist, would not like being taught his business or having suggestions made to him by an elderly spinster lady. Hercule Poirot – a professional sleuth – would not be at home at all in Miss Marple's world."

In 2013, the Christie family supported the release of a new Poirot story, The Monogram Murders, written by British author Sophie Hannah. Hannah later published three more Poirot mysteries, Closed Casket in 2016, The Mystery of Three Quarters in 2018., and The Killings at Kingfisher Hill in 2020.
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