I am an international detective. . . I belong to the world.
from Murder on the Orient Express
Hercule Poirot is Agatha Christie's greatest creation, many say. One of the most famous detectives in all fiction, he was created in 1916 (when Agatha Christie penned the first novel The Mysterious Affair at Styles). The Belgian detective appeared in 33 novels and 65 short stories and is the only fictional character to be honored with a front page obituary of The New York Times.
He doesn't have any disorders to speak of, but demands order. He likes things in an orderly manner (ie, books arranged on a shelf according to height) and approves of symmetry everywhere (residence Whitehaven Mansions is picked because of its symmetry). He despises dust and unclean homes and favors the indoors (especially central heating in the winter). Poirot also values method--to him the greatest method or tool in solving crime is using the "gray cells" of the brain. He derides such methods as examing footprints, collecting cigarette ash, searching for clues with a magnifying glass, or taking fingerprints. He says any crime can be solved with simply placing the puzzle pieces correctly. He is an armchair detective-- he has to simply "sit still in an armchair and think".
Of course, Poirot's mustache is as famous as his "little gray cells". He has pride is his luscious, waxed black mustache and is always meticulously dressed down to his patent leather shoes.
To read more about the world's greatest detective, a great place to start would be Poirot's profile, found here. Poirot has accomplished quite a bit (well, considering he's had a long life). You can read more about Poirot's age here.