Agatha Christie even put that one character in some of the Poirot books who I'd swear was there for the sole purpose of poking fun at Poirot in a meta way.

(You know, Poirot's friend, the mystery writer who complained to him that the main character of her books was too popular for her to not use even though she was utterly sick of him and wished she hadn't given him so many damn quirks that she now had to include.)