An essayist who also writes fiction? Or a fantasist who can't resist nonfiction narrative?
Anyone who has read a collection of Harlan Ellison's short stories has also sampled his work as an essayist; he almost always supplements such collections with introductions, individual prefaces and explanatory notes that sometimes constitute up to half the book's length. To get a true taste for Ellison's supreme talent as a nonfiction writer, however, one must plunge into one of the volumes listed here.