Which famous authoress had the pseudonym of Mary Westmacott?

Dame Agatha Mary Clarissa Christie, Lady Mallowan, DBE (née Miller; 15 September 1890 – 12 January 1976) 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 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.