The "Demon Barber" refers to the fictional character Sweeney Todd, a barber who is known for his dark and sinister actions. He is a central figure in the musical and play titled Sweeney Todd: The Demon Barber of Fleet Street, created by Stephen Sondheim. The story is set in Victorian London and revolves around Todd's quest for revenge against a corrupt judge. In the narrative, Todd operates a barber shop where he lures unsuspecting customers. After cutting their hair, he murders them and collaborates with Mrs. Lovett, who uses the bodies to make meat pies. This gruesome tale explores themes of vengeance, justice, and morality.