Agatha Mary Clarissa, Lady Mallowan, DBE (née Miller; 15 September 1890 – 12 January 1976), commonly known as Agatha Christie, was an English crime writer of novels, short stories and plays. She also wrote romances under the name Mary Westmacott, but is best remembered for her 80 detective novels and her successful West End theatre plays. Her works, particularly featuring detectives Hercule Poirot or Miss Jane Marple, have given her the title the 'Queen of Crime' and made her one of the most important and innovative writers in the development of the genre.
Christie has been called—by the Guinness Book of World Records, among others — the best-selling writer of books of all time and the best-selling writer of any kind, along with William Shakespeare. Only the Bible is known to have outsold her collected sales of roughly four billion copies of novels. UNESCO states that she is currently the most translated individual author in the world with only the collective corporate works of Walt Disney Productions surpassing her. Christie's books have been translated into (at least) 56 languages.
Her stage play, The Mousetrap, holds the record for the longest initial run in the world, opening at the Ambassadors Theatre in London on 25 November 1952, and as of 2008 is still running after more than 23,000 performances. In 1955, Christie was the first recipient of the Mystery Writers of America's highest honor, the Grand Master Award, and in the same year, Witness for the Prosecution was given an Edgar Award by the MWA, for Best Play. Most of her books and short stories have been filmed, some many times over (Murder on the Orient Express, Death on the Nile and 4.50 From Paddington for instance), and many have been adapted for television, radio, video games and comics.
In 1968, Booker Books, a subsidiary of the agri-industrial conglomerate Booker-McConnell, bought a 51% stake in Agatha Christie Limited, the private company that Christie had set up for tax reasons. Booker later increased its stake to 64%. In 1998, Booker sold its shares to Chorion, a company whose portfolio also includes the literary estates of Enid Blyton and Dennis Wheatley.
Agatha Christie was born as Agatha Mary Clarissa Miller in Torquay, Devon, in the United Kingdom. Her parents were Frederick Alvah Miller, a rich American stockbroker, and Clarissa Margaret Boehmer, the English daughter of a British army captain. She never claimed United States citizenship. Christie had a sister, Margaret Frary Miller (1879 – 1950), called Madge, eleven years her senior, and a brother, Louis Montant Miller (1880 – 1929), called Monty, ten years older than Christie. Her father died when she was eleven years old. Her mother taught her at home, encouraging her to write at a very young age. At the age of 16, she went to Mrs Dryden's finishing school in Paris to study singing and piano.
Her first marriage, an unhappy one, was in 1914 to Colonel Archibald Christie, an aviator in the Royal Flying Corps. The couple had one daughter, Rosalind Hicks. They divorced in 1928, two years after Agatha discovered her husband was having an affair. It was during this marriage that she published her first novel in 1920, The Mysterious Affair at Styles.
During World War I she worked at a hospital and then a pharmacy, a job that influenced her work. Many of the murders in her books are carried out with poison.
Eleven days after her disappearance, Christie was identified as a guest at the Hydropathic Hotel (now the Hydro hotel), Harrogate, Yorkshire, where she was registered as 'Mrs Teresa Neele', from Cape Town. Christie gave no account of her disappearance, two doctors having diagnosed her as suffering from amnesia, and opinion remains divided as to the reasons for her disappearance. One suggestion is that she had suffered a nervous breakdown, brought about by a natural propensity for depression, exacerbated by her mother's death earlier that year and by her husband's infidelity. Many people at the time believed the disappearance to be a publicity stunt, and public sentiment was predominantly negative and Edgar Wallace's suggestion that the disappearance was an attempt to embarrass her husband continues to find support, even to the extent of suggestions that Christie was trying to make people believe her husband had killed her in order to punish him for his infidelity.
Christie's travels with Mallowan contributed background to several of her novels set in the Middle East. Other novels (such as And Then There Were None) were set in and around Torquay, Devon, where she was born. Christie's 1934 novel, Murder on the Orient Express was written in the Hotel Pera Palace in Istanbul, Turkey, the southern terminus of the railway. The hotel maintains Christie's room as a memorial to the author. The Greenway Estate in Devon, acquired by the couple as a summer residence in 1938, is now in the care of the National Trust. Christie often stayed at Abney Hall in Cheshire, which was owned by her brother-in-law, James Watts. She based at least two of her stories on the hall: The short story The Adventure of the Christmas Pudding, which is in the story collection of the same name, and the novel After the Funeral. "Abney became Agatha's greatest inspiration for country-house life, with all the servants and grandeur which have been woven into her plots. The descriptions of the fictional Styles, Chimneys, Stoneygates and the other houses in her stories are mostly Abney in various forms.
In 1971 she was made a Dame Commander of the Order of the British Empire.
Agatha Christie died on 12 January 1976, at age 85, from natural causes, at Winterbrook House in the north of Cholsey parish, adjoining Wallingford in Oxfordshire (formerly Berkshire). She is buried in the nearby St. Mary's Churchyard in Cholsey.
Christie's only child, Rosalind Hicks, died on 28 October 2004, also aged 85, from natural causes. Christie's grandson, Mathew Prichard, was heir to the copyright to some of his grandmother's literary work (including The Mousetrap) and is still associated with Agatha Christie Limited.
Her other well known character, Miss Marple, was introduced in The Murder at the Vicarage in 1930, and was based on women like Christie's grandmother and her "cronies" 
During World War II, Christie wrote two novels intended as the last cases of these two great detectives, Hercule Poirot and Jane Marple, respectively. These have been identified as Curtain and Sleeping Murder. Both books were sealed in a bank vault for over thirty years, and were released for publication by Christie only at the end of her life, when she realised that she could not write any more novels. These publications came on the heels of the success of the film version of Murder on the Orient Express in 1974.
Like Arthur Conan Doyle with Sherlock Holmes, Christie was to become increasingly tired of her detective, Poirot. In fact, by the end of the 1930s, Christie confided to her diary that she was finding Poirot “insufferable," and by the 1960s she felt that he was "an ego-centric creep." However, unlike Conan Doyle, Christie resisted the temptation to kill her detective off while he was still popular. She saw herself as an entertainer whose job was to produce what the public liked, and what the public liked was Poirot.
In contrast, Christie was fond of Miss Marple. However it is interesting to note that the Belgian detective’s titles outnumber the Marple titles by more than two to one. This is largely because Christie wrote numerous Poirot novels early in her career, while The Murder at the Vicarage remained the sole Marple novel until the 1940s.
Christie never wrote a novel or short story featuring both Poirot and Miss Marple. In a recording, recently re-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." 
Poirot is the only fictional character to have been given an obituary in The New York Times, following the publication of Curtain in 1975.
Following the great success of Curtain, Christie gave permission for the release of Sleeping Murder sometime in 1976, but died in January 1976 before the book could be released. This may explain some of the inconsistencies compared to the rest of the Marple series — for example, Colonel Arthur Bantry, husband of Miss Marple's friend, Dolly, is still alive and well in Sleeping Murder despite the fact he is noted as having died in books published earlier. It may be that Christie simply did not have time to revise the manuscript before she died. Miss Marple fared better than Poirot, since after solving the mystery in Sleeping Murder she returns home to her regular life in St. Mary Mead.
On an edition of Desert Island Discs in 2007, Brian Aldiss claimed that Agatha Christie told him that she wrote her books up to the last chapter, and then decided who the most unlikely suspect was. She would then go back and make the necessary changes to "frame" that person. The evidence of Christie's working methods, as described by successive biographers, belies this claim.
Twice, the murderer surprisingly turns out to be the narrator of the story, in The Murder of Roger Ackroyd and Endless Night.
On four occasions, Agatha Christie lets the murderer escape justice (and in the latter three stories, implicitly almost approves of the murder), in The Witness for the Prosecution (short story version), Murder on the Orient Express, Curtain and The Unexpected Guest. On a fifth occasion (Taken at the Flood), Poirot exculpates the perpetrator of manslaughter.
Twelve of the stories which were published in The Sketch magazine in 1924 under the sub-heading of The Man who was No. 4 were further joined into one continuous narrative in the novel The Big Four in 1927. Four further stories, The Submarine Plans (1923), Christmas Adventure (1923), The Mystery of the Baghdad Chest (1932) and The Second Gong (1932), were expanded into longer narratives by Christie (respectively The Incredible Theft, The Adventure of the Christmas Pudding, The Mystery of the Spanish Chest and Dead Man's Mirror although the shorter versions of all four have also been published in the UK).
Only one short story remains unpublished in the UK in book form: Three Blind Mice (1948) on which a Christie placed a moratorium whilst the stage play based on the story, The Mousetrap, was still running in the West End.
In the US, the story Christmas Adventure has not been published in book form.
The main collections in both markets are:
In addition, various collections have been published over the years which re-print short stories which have previously appeared in other collections e.g. Surprise, Surprise! (1965 in the US). On occasion, in among the reprinted material, these collections have sometimes contained the first book printing of an individual story e.g. The Market Basing Mystery in the UK version of Thirteen for Luck! (1966) which later appeared in the same market in Poirot's Early Cases.
Agatha Christie's Poirot television series
Episodes include:
HarperCollins independently began issuing this series also in 2007.
In addition to the titles issued the following titles are also planned for release: