The Blagger's Guide To...Professor Moriarty

'He's part master criminal, and part Brian Cox'

*Sherlock Holmes's arch enemy, Professor Moriarty, is at the centre of tonight's third and final episode of the current BBC adaptation (Sherlock: The Reichenbach Fall, BBC1, 9pm).

The episode (which has a fleeting scene of Dr Watson reading The Independent) is based on Sir Arthur Conan Doyle's 1893 story "The Final Problem", and stars the Irish actor Andrew Scott as one of literature's most famous villains. His first words tonight are: "No rush."

*Scott's take on Moriarty is that "People that you're really frightened of, it's usually because you don't know anything about them. You think, 'God I've no idea what he may do'...What is really scary about Moriarty is that he can be right in front of you, hiding in plain sight. There's an audacity about that."

*In this series, and the last (broadcast on BBC1 in three episodes in summer 2010), Moriarty has, so far, only appeared for a total of about 15 minutes.

*Moriarty has been depicted many times on screen, including by: Orson Welles, Spike Milligan, Laurence Olivier, and a holodeck simulation (in two episodes of Star Trek: The Next Generation).

*Although Moriarty is famous as Holmes's nemesis, he appears in person in only two of Conan Doyle's stories: "The Final Problem", in which he is introduced in order to kill off Holmes so that the author can concentrate on more highbrow writing pursuits, and again in "The Valley of Fear" (published in book form in 1915), which is set before Holmes's supposed death and subsequent resurrection.

*According to Holmes, Moriarty is "the celebrated author of 'The Dynamics of an Asteroid', a book which ascends to such rarefied heights of pure mathematics that it is said that there was no man in the scientific press capable of criticising it". Unfortunately, he also "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."

*There is little in the stories to describe Moriarty physically, except to say that he had "a high, domed forehead" – a feature that was believed to indicate great intellectual ability.

*Among Conan Doyle scholars and Holmes fans there has been much speculation that Moriarty was based on two people: Adam Worth, an international master criminal, and the US astronomer, mathematician and multi-talented genius Simon Newcomb – a sort of 19th-century Brian Cox.

*Moriarty is "the Napoleon of Crime, the greatest schemer of all time, the organiser of every devilry, the controlling brain of the underworld, a brain which might have made or marred the destiny of nations".

*At the end of the Conan Doyle story on which tonight's episode is based, both Holmes and Moriarty are presumed (by Watson) to have fallen to their deaths in the Alps. At the real Reichenbach Falls in Switzerland, a plaque reads: "At this fearful place, Sherlock Holmes vanquished Professor Moriarty, on 4 May 1891." Eventually, owing to popular demand, Conan Doyle brought back Holmes in "The Hound of the Baskervilles" (serialised in The Strand Magazine in 1901 and 1902), revealing that he did not die but lay low. The BBC will not reveal whether there will be a third series of Sherlock.