An American, Lawrence Block, wrote lots of books: Wikipedia includes this:
This is Block's salute to the Nero Wolfe series created by Rex Stout. The character Chip Harrison is a take on Wolfe's assistant, Archie Goodwin. In the series, Block created Leo Haig, a character who openly models himself after Nero Wolfe, imitating most of Nero Wolfe's peculiarities such as refusing to leave his residence on business, sending out his associate instead to do the "legwork," and copying Wolfe's habits, such as obsession with plants but substituting the object of affection with tropical fish instead.
Block's Haig believes that Nero Wolfe and Archie Goodwin actually exist in real life, living and operating under pseudonyms; that Rex Stout was only a chronicler and one pseudonym of Archie Goodwin; and that if Haig proves himself worthy, Wolfe will invite Haig to dinner.
Having read all publications on Wolfe, Haig operates as he imagines Wolfe would, and assigns Chip Harrison tasks as Wolfe would assign Goodwin.