Professor Moriarty is Sherlock Holmes’s arch-enemy: a brilliant mathematician turned “Napoleon of crime” who secretly controls much of London’s underworld while posing as a respectable professor.

Who was Moriarty in Sherlock Holmes?

In Arthur Conan Doyle’s original stories, Professor James Moriarty is a fictional criminal mastermind created specifically to be a nemesis formidable enough to destroy Holmes. Doyle introduced him in “The Final Problem” (1893), where Holmes describes him as the unseen organizer behind numerous major crimes, operating through intermediaries so he is almost never seen or caught.

Moriarty is portrayed as Holmes’s intellectual equal but moral opposite: a genius-level mathematician who once held a university chair and published works such as a treatise on the binomial theorem, before applying his talents entirely to crime. Holmes famously calls him the “Napoleon of crime,” stressing that individual criminals are just “little cogs” in the vast machine Moriarty runs from the shadows.

Their most famous encounter is at the Reichenbach Falls in Switzerland, where Holmes and Moriarty struggle and are believed to fall to their deaths; Doyle used this to (temporarily) kill off Holmes. Later, in “The Adventure of the Empty House,” it is revealed that Holmes survived by faking his death, while Moriarty’s criminal network continues to loom in the background of the Holmes universe.

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