Which fictional detective lives at 221B Baker Street?

The fictional detective who lives at 221B Baker Street is Sherlock Holmes. Sir Arthur Conan Doyle introduced Holmes and Dr. John Watson as lodgers at the London address in A Study in Scarlet, published in 1887.

In the stories, 221B is a suite of rooms above a lodging house run by Mrs. Hudson. Holmes uses the rooms as both home and consulting office, while Watson becomes his companion, chronicler, and occasional medical adviser. The address quickly became one of the most recognisable locations in detective fiction.

The number was fictional when the stories were first published; Baker Street did not then extend to 221. After street numbering changed, the Abbey National building occupied the relevant block and received large quantities of mail addressed to Holmes. The organisation even employed a secretary to respond to some of it.

Today, the Sherlock Holmes Museum uses the 221B designation by permission, although its building lies between actual addresses 237 and 241 Baker Street. Sam Spade, Philip Marlowe, and Hercule Poirot are detectives associated with other fictional worlds.