Hercule Poirot (pronounced /ɜrˈkjuːl pwɑrˈoʊ/; French pronunciation: [ɛʁkyl pwaʁo]) is a fictional Belgian detective, likely a Walloon created by Agatha Christie. Along with Miss Marple, Poirot is one of Christie's most famous and long-lived characters, appearing in 33 novels and 51 short stories that were published between 1920 and 1975 and set in the same era.

Poirot has been portrayed on radio, on screen, for films and television, by various actors including John Moffatt, Albert Finney, Peter Ustinov, Ian Holm, Tony Randall, Alfred Molina and David Suchet.

His name was derived from two other fictional detectives of the time: Marie Belloc Lowndes' Hercule Popeau and Frank Howel Evans' Monsieur Poiret, a retired Belgian police officer living in London. Hercule Poirot's initials replicate that of the sauce which he happens to like, HP Brown Sauce as he comments in Elephants Can Remember: "Ah yes, that is correct my initials do appear to be the same as such a fine delicacy, a good English creation." A more obvious influence on the early Poirot stories is that of Arthur Conan Doyle. In An Autobiography Christie admits that "I was still writing in the Sherlock Holmes tradition –eccentric detective, stooge assistant, with a Lestrade-type Scotland Yard detective, Inspector Japp." For his part Conan Doyle acknowledged basing his detective stories on the model of Edgar Allan Poe's C. Auguste Dupin, and his anonymous narrator, and based his character Sherlock Holmes on Joseph Bell, who in his use of "ratiocination" prefigures Poirot's reliance on his "little grey cells".

Poirot also bears a striking resemblance to A. E. W. Mason's fictional detective—Inspector Hanaud of the French Sûreté—who, first appearing in the 1910 novel At the Villa Rose predates the writing of the first Poirot novel by six years. In chapter 4 of the second Inspector Hanaud novel, The House of the Arrow (1924), Hanaud declares sanctimoniously to the heroine, "You are wise, Mademoiselle…For, after all, I am Hanaud. There is only one."

Christie's Poirot was Belgian. Unlike the models mentioned above, Christie's Poirot character was clearly the result of her early development of the detective in her first book written in 1916 (although not published until 1920). Not only was his Belgian nationality interesting because of Belgium's occupation by Germany (which provided a valid explanation of why such a skilled detective would be out of work and available to solve mysteries at an English country house), but also at the time of Christie's writing, it was considered patriotic to express sympathy with the Belgians, since the invasion of their country had constituted Britain's casus belli for entering World War I, and British wartime propaganda emphasized the "Rape of Belgium".

His first published appearance was in The Mysterious Affair at Styles (published 1920) and his last was in Curtain (published 1975, the year before Christie died). On publication of this novel, Poirot was the only fictional character to be given an obituary in the New York Times; August 6, 1975 "Hercule Poirot is Dead; Famed Belgian Detective".

By 1930, Agatha Christie found Poirot 'insufferable' and by 1960, she felt that he was a 'detestable, bombastic, tiresome, ego-centric little creep'. Yet the public loved him, and Christie refused to kill him off, claiming that it was her duty to produce what the public liked, and what the public liked was Poirot.

Here is how Captain Arthur Hastings first describes Poirot:

This is how Agatha Christie describes Poirot in The Murder on the Orient Express in the very initial pages:

In the later books, the limp is not mentioned, which suggests it may have been a temporary wartime injury. Poirot has dark hair, which he dyes later in life (though many of his screen incarnations are portrayed as bald or balding) and green eyes that are repeatedly described as shining "like a cat's" when he is struck by a clever idea. Frequent mention is made of his patent-leather shoes, damage to which is frequently a subject of (for the reader, comical) misery on his part. Poirot's appearance, regarded as fastidious during his early career, is hopelessly out of fashion later in his career.