In which episode does Jim Moriarty first appear in BBC Sherlock?

Jim Moriarty first appears in BBC Sherlock in the episode “The Great Game.” He is introduced as the mysterious criminal mastermind orchestrating the episode’s chain of timed puzzles, murders and hostage situations.

“The Great Game” is the third and final episode of Sherlock’s first series, first broadcast on BBC One on 8 August 2010. Moriarty initially appears indirectly through the cases confronting Sherlock, with the victims and clues suggesting that a single hidden criminal is manipulating events. The episode eventually reveals that he is the “consulting criminal” behind the game and brings him face to face with Sherlock.

Andrew Scott plays Moriarty, giving the character an energetic and unnerving modern interpretation of Sherlock Holmes’s classic enemy. The episode ends on a cliffhanger: Moriarty leaves, but returns after Sherlock removes John Watson’s explosive vest, while snipers keep both men trapped. Viewers sometimes confuse this with “The Reichenbach Fall,” where Moriarty becomes the central antagonist, but that later episode develops a character who was already introduced in “The Great Game.”