Before the 1850s, letters didn't have separate envelopes. They were folded so the contents of the letter were on the inside, and the address on the outside. (source)
Arthur Conan Doyle admitted that his super-famous detective Sherlock Holmes was based on Dupin. Read all about it in a New York Times article from 1909. (source)
Author Mathew Purl makes Dupin a main character in his novel The Poe Shadow.
Looks like Poe had some real-life detective skills: he solved the mystery in a story by Charles Dickens. Check out the New York Times reporting on it in 1913. (source)
Dupin is on a Nicaraguan Stamp! Don't ask us why. (source)