Jamie Moriarty

"You look at people and you see puzzles. I see games. You? You're a game I'll win every time."

- Jamie Moriarty to Sherlock Holmes

Jamie Moriarty, initially known to Sherlock as Irene Adler, is the hidden mastermind behind Sebastian Moran, the main antagonist of Elementary. She is a criminal mastermind and the nemesis of Sherlock Holmes.

Moriarty is at first thought to be directly responsible for the death of Holmes' lover, Irene Adler. Moriarty is also responsible for 70 murders over her career. It is originally assumed that Moriarty is a man, due in part to her getting a man to speak on the phone for her. It is later revealed that Moriarty and Irene Adler are one and the same.

Overview
As Irene, she is Sherlock's former lover, while in her true identity as Moriarty she is a criminal mastermind who romanced Sherlock—and then faked Irene's death—to draw his investigations away from her criminal activities. It was her supposed death as Irene that caused Sherlock's already established drug use to escalate.

"Irene" is first introduced as an optimistic, sexual, beautiful, artsy and quirky woman who showed a bright side of life to Holmes. It doesn't last. Her "death" led Holmes to addiction and destroyed his life and career in London. Just to get better, two years later Holmes discovers that she was faking everything and "Irene" never existed at all. Her persona was meticulously constructed to fool Holmes and push him away from her plans, and her "death" was designed to break him.

Despite Sherlock discovering her true identity, and her subsequent imprisonment, the two continue to have conflicting feelings for each other—Holmes noting during a conversation with Bell that "the love of [his] life is an unrepentant homicidal maniac"—and great mutual respect for each other's intellectual powers.

Even if she is lack of sympathy and morality, Moriaty is not a Complete Monster. Her one unambiguously good act was giving up her daughter for adoption at birth, knowing full well that not only would a child interfere with her career but that her career plus evil nature would make her a terrible mother for the child, and she actually did want better for the girl. She has also gained an amount of respect for Joan Watson, as the latter's ability to fool her is what got her arrested; when Joan's life is threatened by drug kingpin Elana March, she arranges the criminal's death in her cell.

At the end of Season 4, Sherlock's father, Morland Holmes, took over Moriarty's crime orginization which will help him to dismantle the group and guarantee safety of his son from further harm.

Trivia

 * She is portrayed by Natalie Dormer.
 * Despite being the true main antagonist of the show, Moriarty only appears in 4 episodes in the flesh, and in 2 others only as a voice-over.
 * She is a composite character of the original Professor James Moriarty and Irene Adler, and had significant changes on both sides:
 * James Moriaty: She is the first female version of Moriarty and also the main hero's former lover. This version of Moriarty has a more personal connection to Holmes than just being his rival. In addition to being a criminal mastermind, she also seduced him with a false persona, causing the reveal of her true nature to hit him close to home.
 * Irene Adler: In the original stories, Irene was nothing more than an unusually clever opera singer who happened to get her hands on a compromising photograph, and was smart enough to prevent Holmes from stealing it back. Here, she's a persona deliberately created by her true identity, Moriarty, to seduce and fool Holmes.