Claim: Agatha Christie wrote professionally.

Dame Agatha Mary Clarissa Christie , Lady Mallowan , DBE -LRB- née Miller ; 15 September 1890 -- 12 January 1976 -RRB- was an English crime novelist , short story writer and playwright . She is best known for her 66 detective novels and 14 short story collections , particularly those revolving around her fictional detectives Hercule Poirot and Miss Marple . She also wrote the world 's longest-running play , a murder mystery , The Mousetrap , and six romances under the name Mary Westmacott . In 1971 she was made a Dame for her contribution to literature .   Christie was born into a wealthy upper-middle-class family in Torquay , Devon . She served in a Devon hospital during the First World War , tending to troops coming back from the trenches , before marrying and starting a family in London . She was initially an unsuccessful writer , but this all changed for the better when The Mysterious Affair at Styles was published in 1920 featuring Hercule Poirot . During the Second World War she worked as a pharmacy assistant at University College Hospital , London during the Blitz and acquired a good knowledge of poisons which featured in many of her novels .   Guinness World Records lists Christie as the best-selling novelist of all time . Her novels have sold roughly 2 billion copies , and her estate claims that her works come third in the rankings of the world 's most-widely published books , behind only Shakespeare 's works and the Bible . According to Index Translationum , she remains the most-translated individual author -- having been translated into at least 103 languages . And Then There Were None is Christie 's best-selling novel , with 100 million sales to date , making it the world 's best-selling mystery ever , and one of the best-selling books of all time .  Christie 's stage play The Mousetrap holds the world record for longest initial run . It opened at the Ambassadors Theatre in the West End on 25 November 1952 and is still running after more than 25,000 performances .   In 1955 , Christie was the first recipient of the Mystery Writers of America 's highest honour , the Grand Master Award . Later the same year , Witness for the Prosecution received an Edgar Award by the MWA for Best Play .  In 2013 , The Murder of Roger Ackroyd was voted the best crime novel ever by 600 fellow writers of the Crime Writers ' Association . On 15 September 2015 , coinciding with her 125th birthday , And Then There Were None was named the `` World 's Favourite Christie '' in a vote sponsored by the author 's estate . Most of her books and short stories have been adapted for television , radio , video games and comics , and more than thirty feature films have been based on her work .