Hercule Poirot (pronounced 'Erkyl Pwaro'), with his "little grey cells", was Agatha Christie's most famous detective creation, easily eclipsing Miss Marple, Parker Pyne and Tommy & Tuppence.
A short man, he had a head exactly the shape of an egg, always perched a little to one side. His "moustaches" were his pride and joy, and over the years and dozens of novels and short stories, he spent a fair amount of time waxing them, stroking them and even dying them black in an effort to look younger.
He was a very neat and overly fastidious person: not only would "a speck of dust cause him more pain than a bullet wound", he also requested his morning toast be cut in neat little squares to accompany his breakfast cup of chocolate.
Poirot's death at the age of at least 125 in Curtain (1975) was announced in The New York Times in a front page obituary. Agatha Christie had wanted to kill him off from about 1930, soon after creating him. Christie thought he was a "detestable, bombastic, tiresome, egocentric little creep", but continued to write about him as he was so loved by her massive fan base.
Some of my personal favourite Poirot novels: Appointment with Death (1937), Lord Edgeware Dies (1933), Poirot's Early Cases (1974), The Labours of Hercules (1947).