Professor Moriarty is a fictional character created by Sir Arthur Conan Doyle. He is best known as the arch-nemesis of Sherlock Holmes, the famous detective. Moriarty is often depicted as a criminal mastermind, orchestrating a vast network of crime in London. His intelligence and cunning make him a formidable opponent for Holmes. Moriarty first appears in the story "The Final Problem," where he is portrayed as a brilliant strategist who poses a significant threat to Holmes. He is often referred to as the "Napoleon of crime," highlighting his strategic mind and ability to manipulate others for his own gain.