James Moriarty

Professor James Moriarty was the arch-enemy of Sherlock Holmes.

Jimmy Moriarty, time traveller
By one account, "Jimmy Moriarty" was a 21st century scientific genius who was given a method of ritualistic time travel by the Celestis during the War in Heaven. Moriarty conducted a first time experiment by sending Thomas Corkle to the late 19th century to try to prevent Sherlock Holmes from becoming a successful detective. (PROSE: Erasing Sherlock)

Mathematical career
In what was assumed to be his native 19th century, Professor Moriarty was a mathematician, whose work on the binomial theorem impressed the Académie Francaise. (PROSE: The Death of Art) He wrote a paper on the mathematics of folding higher dimensions (PROSE: All-Consuming Fire) and his book On the Dynamics of the Asteroid (PROSE: The Death of Art, The Book of the Enemy) first introduced the theory of relativity. (PROSE: The Book of the Enemy)

Opposing Sherlock Holmes
Moriarty, however, was also at the head of a criminal organization that had control of most of Britain's underworld in Sherlock Holmes's lifetime, causing the two to become bitter enemies. Under the guise of the red-haired, mild-mannered Mr O'Connor, he once traveled to India alongside Holmes and Dr Watson — as well as the Seventh Doctor and Bernice Summerfield — to investigate the schemes of Baron Maupertuis. Maupertuis had in fact been recruiting an army from the criminal classes with which to conquer the alien planet Ry'leh in the name of the British Empire, hence Moriarty's anger, as the Baron was essentially filling his army by depleting Moriarty's own.

Once he learned that Maupertuis' armies had already gone through the dimensional portal and were being slaughtered by the Shlangii guarding Azathoth, however, Moriarty returned to England, deeming them a lost cause. Before he did so, he briefly had a conversation with Watson, during which he admitted, first, that he expected nothing of the world to begin with, hence his lack of surprise at the discovery of extraterrestrial life, and secondly, that he "did not wish to be understood by the world, only noticed". Watson thought that this might provide "the key to [Moriarty's] character". (PROSE: All-Consuming Fire)

He died in 1893. (PROSE: The Found World)

Reduced to fiction
Sherlock and his adventures were turned into fiction by agents in the War in Heaven (PROSE: The Book of the Enemy) Many scholars believed that Arthur Conan Doyle based the character of Moriarty after Simon Newcomb. (PROSE: The Baker Street Dozen)

At any rate, Holmes and Moriarty, now being fictional characters in the writings of Arthur Conan Doyle, thus gained existence in the Land of Fiction. There, he became the chairman of a "gentlemen's club" of literary villains called the Sisyphean Society, scheming to acquire the headband which would make him Master of the Land of Fiction. In the course of this scheme, however, he was confronted with, who had traveled to the Land of Fiction and infiltrated the club.

The Master overpowered Moriarty by making him realise his status, within Doyle's works, as a mere plot device to kill Holmes, and an unsuccessful one at that. This caused Moriarty to revert to his literary fate, namely death by falling down the Reichenbach Fall. The Master then took the headband for himself and brought it back to the "real world", as he knew ruling over mere fictions (albeit sentient ones) would be unsatisfying. (COMIC: Character Assassin)

A number of Moriarty Remakes were also created in the City of the Saved based on the fictional Moriarty character. Many of them attacked the Great Detective Agency, a congregation of Sherlock Holmes Remakes. (PROSE: Eliminating the Impossible, The Baker Street Dozen)

Behind the scenes

 * Moriarty has been played by Paul Freeman in the film Without a Clue, Philip Locke on stage and Ronald Pickup in a radio play.
 * Doctor Who producer Barry Letts and script editor Terrance Dicks confirmed that the Master was devised as "the Moriarty" to the Doctor's "Sherlock Holmes". (DOC: Life on Earth) Scott Gray explained in the Oblivion trade paperback that this comment inspired his story Character Assassin in which actually confronts (and easily defeats) the original Moriarty.
 * Meanwhile real-life article The Daleks: Story of a Phenomenon in Terry Nation's Dalek Special described the Daleks' as the Doctor's equivalent to what Moriarty is to Sherlock Holmes.