Agatha Christie, who died on 12 January, 1976, at the age of 85, was the most successful and popular crime fiction writer of the 20th century.

Her 80 detective novels, many featuring the deductive talents of Hercule Poirot and Miss Marple, have sold over two billion copies around the world, giving her the undisputed reputation of 'Queen of Crime'.

The Guinness Book of Records lists her as the biggest selling author of books in history and the best-selling writer of any kind second only to William Shakespeare. She also wrote romantic fiction (under the name Mary Westmacott), short stories, poetry and plays for the stage, screen and radio.

Her mystery play The Mousetrap holds the record for the longest ever run in London, opening at the Ambassadors Theatre on 25 November, 1952, and still running as of 2009, with nearly 23,000 performances to date. Most of her books have been adapted for television and the cinema.

She was born as Agatha Mary Clarissa Miller in Torquay, Devon, on 15 September, 1890. Her parents were Frederick Miller, a wealthy American stockbroker, and Clara Boehmer, a British aristocrat. She had a brother and sister, both more than 10 years her senior. Christie’s father died when she was very young.

She was largely taught at home by her mother who encouraged her to write from an early age. At 16 she went to a school in Paris to study singing and piano. She worked at a hospital and pharmacy during the First World War which was probably where she gained the knowledge to write the various poisonings in her books.

In 1914 she married aviator Colonel Archibald Christie. The marriage lasted 14 years and produced a daughter, Rosalind, but it ended in divorce in 1928.

His first novel, The Mysterious Affair at Styles, was published in 1920. It featured the Belgian detective Hercule Poirot, a character who would feature in more than 30 novels, and 50 short stories, including Murder on the Orient Express, her most famous work. The Poirot stories were highly influenced by Sir Arthur Conan Doyle, featuring a Watson-style narrator, Arthur Hastings.

Ten years later, Miss Marple made her first appearance in The Murder at the Vicarage. Marple, an elderly spinster from the village of St Mary Mead, was based on Mrs Christie’s grandmother. Miss Marple became a nicer, more-likeable character over the years and would use her disarming countenance to her advantage when solving crimes.

Poirot and Marple never met, but many fans believe they co-existed in the same "world" as some characters appear in stories involving both detectives.

The pair were both killed off by Mrs Christie shortly before her own death in 1976, though she had been tempted to kill Poirot many times, describing him as "insufferable" and an "an ego-centric creep" at various points of her career. In fact, the novels that covered Poirot and Marple’s "final cases" were both written in the 1940s and locked away in a bank vault until the author saw fit to publish them.

Mrs Christie had married a second time in 1930, this time to the archaeologist Sir Max Mallowan.

In her long career, to which the adjective illustrious sounds like an understatement, Agatha Christie received many accolades, including first Mystery Writers of America Grand Master Award in 1955. She was made a Dame in 1971.

She died of natural causes in 1976 at Winterbrook House in Oxfordshire and is buried in the nearby St Mary's Churchyard in Cholsey