Professor James Moriarty was a fictional character from the 19th century Sherlock Holmes novels by Sir Arthur Conan Doyle. He was an adversary to Sherlock Holmes, a man with knowledge equal to Holmes'.
Katherine Pulaski read Sherlock Holmes novels in her youth, and was always frightened by the despicable Moriarty.
A hologram based on Moriarty was created on board the USS Enterprise-D in 2365.
In 2369, when the holographic Moriarty appeared to gain the ability to exit the holodeck, Captain Picard warned him that the criminal behavior shown in the novels would not be acceptable in the 24th century. The holographic Moriarty assured him that he was not the same as the fictional character from the "scribblings of an Englishman dead for four centuries."