2. Jim Moriarty
No list of Sherlock supporting characters would be complete without Jim Moriarty. He is the Joker to Sherlock's Batman. The Moriarty in Conan Doyle's short stories is brilliant but never feels truly dangerous. Andrew Scott's Moriarty on the other hand is both terrifying and funny and interesting all at the same time. He casts a long shadow over the entire series. He acts as benefactor to both the Taxi Driver and the Black Lotus gang. Irene Adler is in his employ and he sets up a tantalising series of clues for Sherlock in The Great Game. His figure manages to be threatening all throughout the show, all the more remarkable when you consider he only has around 15 minutes of screen time before the Reichenbach Fall. Moriarty seems to have an element of control over Sherlock that always keeps the audience guessing. Hell, he almost manages to convince us that Sherlock has invented him to satisfy his twisted bloodlust. It is incredibly difficult even to imagine series three without Jim Moriarty and so he deserves his place as a supporting character who stole the show.