James Moriarty

"He is a man of good birth and excellent education, endowed by nature with a phenomenal mathematical faculty. At the age of twenty-one he wrote A Treatise on the Binomial Theorem, which has had a European vogue. On the strength of it he won the mathematical chair at one of our smaller universities, and had, to all appearances, a most brilliant career before him. But the man had hereditary tendencies of the most diabolical kind. A criminal strain ran in his blood, which, instead of being modified, was increased and rendered infinitely more dangerous by his extraordinary mental powers. Dark rumours gathered round him in the University town, and eventually he was compelled to resign his chair and come down to London. He is the Napoleon of Crime, Watson, the organiser of half that is evil and nearly all that is undetected in this great city..."

- Sherlock Holmes about Professor Moriarty in "The Final Problem"

Professor James Moriarty is the archenemy of Sherlock Holmes and is often considered one of the first supervillains in fiction - he appeared in only two novels and despite rarely encountering Holmes personally he is considered the main antagonist of the entire Sherlock Holmes series and is famously described as the "Napoleon of Crime".

Professor Moriarty is a criminal genius equal to Holmes in brilliance and was famous for being the villain that Sherlock Holmes fought and apparently fell to his doom with in The Final Problem - however due to a large public outlash Arthur Conan Doyle was forced to retcon these events so that both Holmes and Moriarty did not die as was originally planned but rather miraculously survived so that the series could continue.

Moriarty is mentioned but not seen in the novella The Valley of Fear, which is set before "The Final Problem." Here he is depicted as running a "criminal consulting agency," which liaises with various criminal organizations. Moriarty arranges the death of John Douglas, a former Pinkerton detective, as a favor for the Vermissa Valley Gang, a group of corrupt union officials who had been arrested by Douglas. Moriarty's men killed Douglas in spite of Holmes's attempt to save him, an act which puts Holmes forever at odds with Moriarty.

It's also depicted that he has obsession for technology. In the League of Extraordinary Gentlemen, he tricks the league and builds a war airship using the technology he got from his enemies, like Fu Manchu for example. He also brings with him a specialy designed Air Rifle that is disguised as a cane and is perfect for sniping.

Sherlock Holmes: A Game of Shadows
Moriarty also appears in the 2011 movie Sherlock Holmes: A Game of Shadows. Here he serves as the main antagonist of the movie. His version, complete with beard, bears a strong resemblance to purported Moriarty inspiration Adam Worth. During the film he attempts to provoke a war using advanced weaponry that he has developed while sending an assassin into a crucial conference using an early form of plastic surgery. With Watson having deduced his assassin's identity while Moriarty is occupied in a chess game with Holmes, Moriarty and Holmes clash, with the fight ending as Holmes pulls Moriarty over the edge of a balcony into a waterfall, knowing that he cannot defeat Moriarty in a direct fight due to a recent injury and wanting to protect Watson from Moriarty's revenge (Although Holmes is later revealed to have survived).

Other Depictions of Moriarty
In Alan Moore's series The League of Extraordinary Gentlemen, Moriarty serves as the villain of Volume 1 where he deceives the League through Campion Bond into stealing the Cavorite that he uses to power his great warship. He engages The Doctor (Fu Manchu) in a sky battle over Limehouse. He is foiled when Murray smashes the container that holds the Cavorite which starts to float towards the atmosphere. Refusing to lose such a potent part of his plan, Moriarty clings to the Cavorite and subsequently drifts into outer space. In a later volume Century: 1910, he is found frozen solid in space while still clinging to the Cavorite.