, (née ; 15 September 1890 – 12 January 1976) was an English writer known for her sixty-six detective novels and fourteen short story collections, particularly those revolving around fictional detectives and . She also wrote the world's longest-running play, , which was performed in the from 1952 to 2020, as well as six novels under the pseudonym . In 1971, she was appointed a Dame Commander of the Order of the British Empire (DBE) for her contributions to literature. lists Christie as the best-selling fiction writer of all time, her novels having sold more than two billion copies.

Christie was born into a wealthy upper-middle-class family in , Devon, and was largely home-schooled. She was initially an unsuccessful writer with six consecutive rejections, but this changed in 1920 when , featuring detective Hercule Poirot, was published. Her first husband was ; they married in 1914 and had one child before divorcing in 1928. During both World Wars, she served in hospital dispensaries, acquiring a thorough knowledge of the poisons which featured in many of her novels, short stories, and plays. Following her marriage to in 1930, she spent several months each year on in the Middle East and used her first-hand knowledge of his profession in her fiction.

According to , she remains the . is one of the of all time, with approximately 100 million sales. Christie's stage play The Mousetrap holds the world record for the longest initial run. It opened at the in the West End of London on 25 November 1952, and by September 2018 there had been more than 27,500 performances. The play was closed down in March 2020 due to the .

In 1955, Christie was the first recipient of the 's . Later that year, received an for best play. In 2013, she was voted the best crime writer and the best crime novel ever by 600 professional novelists of the . In September 2015, And Then There Were None was named the "World's Favourite Christie" in a vote sponsored by the author's estate. Most of Christie's books and short stories have been adapted for television, radio, video games, and graphic novels. More than thirty feature films are based on her work.

Educated at home by her mother, Christie began writing detective fiction while working as a nurse during . Her first , The Mysterious Affair at Styles (1920), introduced , her and egotistic Belgian detective; Poirot reappeared in about 25 novels and many short stories before returning to Styles, where, in Curtain (1975), he died. The elderly spinster , her other principal detective figure, first appeared in Murder at the Vicarage (1930). Christie's first major recognition came with The Murder of Roger Ackroyd (1926), which was followed by some 75 novels that usually made best-seller lists and were serialized in popular magazines in and the United States.

Christie's plays include (1952), which set a world record for the longest continuous run at one theatre (8,862 performances—more than 21 years—at the Ambassadors Theatre, London) and then moved to another theatre, and Witness for the Prosecution (1953), which, like many of her works, was adapted into a (1957). Other notable film include Murder on the Orient Express (1933; film 1974 and 2017) and Death on the Nile (1937; film 1978). Her works were also adapted for television.

In 1926 Christie's mother died, and her husband, Colonel Archibald Christie, requested a divorce. In a move she never fully explained, Christie disappeared and, after several highly publicized days, was discovered registered in a hotel under the name of the woman her husband wished to marry. In 1930 Christie married the archaeologist Sir Max Mallowan; thereafter she spent several months each year on expeditions in and with him. She also wrote nondetective novels, such as Absent in the Spring (1944), under the pseudonym Mary Westmacott. Her Autobiography (1977) appeared posthumously. She was created a Dame of the in 1971.

Agatha Christie's family members:

Spouse/Ex-: Archibald Christie (M. 1914–1928), Max Mallowan (M. 1930–1976)

Father: Frederick Alvah Miller

Mother: Clarissa Margaret Boehmer

Siblings: Louis Montant Miller, Margaret Frary Miller

Children: Rosalind Hicks