The nemesis of Benedict Cumberbatch's titular main character in Sherlock, Moriarty's alleged death was the lynchpin of the shocking events of the show's second-series finale.
After luring Sherlock to the rooftop of St. Bartholomew's Hospital, Moriarty tells Sherlock that his friends and colleagues will be killed by his assassins unless Sherlock himself commits suicide. Only Moriarty has the fail-safe, as he tells Sherlock, "As long as I am alive, you can save your friends." He then shoots himself in the head and falls to the ground.
Sherlock also fakes his suicide at the end of the second series, but is revealed at the beginning of the third series to be alive and well. It's not until the conclusion of series three that Moriarty resurfaces, his image broadcast across every screen in London, uttering the creepy caption: "Miss Me?"
BBC One recently tweeted an official Sherlock photo, teasing the new series, which may deal with Moriarty's "reappearance."