"The door opened and Professor Moriarty stood before me", The Final Problem
Sherlock Holmes on Moriarty:
“His career has been an extraordinary one. He is a man of good birth and excellent education, endowed by nature with a phenomenal mathematical faculty. ... 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 ..."
“He is the Napoleon of crime, Watson. He is the organizer of half that is evil and of nearly all that is undetected in this great city. He is a genius, a philosopher, an abstract thinker. He has a brain of the first order. He sits motionless, like a spider in the center of its web, but that web has a thousand radiations, and he knows well every quiver of each of them".
- The Final Problem, The Memoirs of Sherlock Holmes
These passages on Moriarty are some of my favourite in the entire Canon. And there is no way I could finish this post without posting a photo of one of the most recent, and in my humble opinion, one of the best incarnations of Moriarty ever, Andrew Scott (and yes, I admit, I am a trifle biased!).
Photo credit: http://blogtorwho.blogspot.com/2011/12/sherlock-promo-pics_22.html
For non-Sherlockians and non-Holmesians, Sherlock Series 2, Episode 3, The Reichenbach Fall, will be based on the Canon story, The Final Problem.