A

"Buckle up bitches, nothing is as it seems..."

- A

"I buried your mom the same way I watched her bury you..."

- 'A' taunting Alison

"A" is the main antagonist of the Freeform original series "Pretty Little Liars". They are an anonymous Big Bad that target the main characters, the Liars, for their own motive and will stop at nothing to get what they want.

While there have been multiple of them, the original and first main "A" was revealed in the second season finale to be Mona Vanderwaal, the Liars' ally. Her helper was Lucas Gottesman. When Mona is sent to Radley Sanitarium for treatment, she is approached by an unknown person who wants to form a partnership, and that person becomes the second main "A", known as Big "A".

Mona and Big "A" form the "A-Team", hiring Toby Cavanaugh, Spencer Hastings, Darren Wilden and Melissa Hastings. After Toby and Spencer leave the team, Big "A" steals the game from Mona and kicks her out of the team, where she becomes one of the Liars herself. Big "A" gains their own personal helper and the "A-Team" disbands after they murder Wilden for betraying them and Melissa leaves. In the 6A finale, Big "A" is unmasked as CeCe Drake, with her helper being Sara Harvey. The two of them were Red Coat. In Season 6B after the five year jump, Charlotte is murdered and this spawns the birth of the third main and final "A", known as Uber "A", who wants to find her killer and get revenge. They hire Jenna Marshall and others as their helpers. In Season 7, it was revealed that Charlotte had a second helper, who was Noel Kahn.

History
In October 2008, Mona Vanderwaal began sending Alison DiLaurentis anonymous threats. Mona sent Alison dolls and stalked her and the Liars, while wearing a zombie baby costume. On Halloween night, Mona attacked Alison, who believed she was Noel Kahn, and crowned herself as "A". Mona's threats as "A" grew stronger and darker and Alison became fearful. On Labor Day weekend of 2009, Mona began sending Alison murder threats to scare her. Various angry people were in Alison's yard and Alison ended up getting hit with a stone by CeCe Drake, who thought she was Bethany Young. Mona, in turn, hit Bethany, believing her to be Alison. Alison survived the incident and was found by Mona on the side of the road, who then convinced her to disappear. Mona finally had everything she wanted and became best friends with Hanna Marin, with both of them becoming the Queen Bees of Rosewood High. Alison's disappearance drew her friends apart and Aria moved away to Iceland. A year after the disappearance, Aria returned to Rosewood and Mona feared that she would lose Hanna to them. So in order to keep them apart, she began using "A" again. She hired help from Lucas Gottesman, blackmailing into being her helper. However, Mona's plan backfired when she actually ended up bringing them closer together. This made Mona even angrier and she eventually began pretending to receive threats from "A" herself. Gaining the Liars trust, Mona began working with them and she and Spencer went out to the Lost Woods Resort to find a clue on "A". Mona ends up revealing herself as "A" to Spencer and tries to convince Spencer to join the A-Team. Meanwhile, at the Ball, the other Liars follow Melissa Hastings, who Mona sent to the Ball, dressed anonymously as the Black Swan. Mona and Spencer fight and Mona ends up falling off of a cliff, but she survives and is admitted to Radley Sanitarium. Here, CeCe Drake begins visiting her and Mona tells her all about the "A" game. CeCe offers her a partnership and they become "A" together, starting a full A-Team, which consists of Toby Cavanaugh, Spencer Hastings, and a blackmailed Lucas and Melissa again. CeCe begins to believe that her cousin and adoptive sister, Alison, is alive and begins disguising herself as Red Coat. She hatches a plan to draw Alison out and forms an alliance with Sara Harvey, who she sends to act as a decoy Red Coat on the night of the Thornhill Lodge party. Their plans are foiled when Shana Fring sets the Lodge ablaze, but it manages to work, as Alison rescues Hanna from the fire, proving she is alive and the other Red Coat.

Later, Shana was killed by The Liars in self-defense when she attempted to finish the job to kill them. Seeing this as the perfect opportunity to end the game, as the Liars thought Shana was "A", Cece prepared to leave for Paris. However, Cece has an addiction to the game, and decided to stick around. After kidnapping the Liars, and mentally torturing them in a dollhouse, she later kidnapped Alison to explain her story. After finishing, Cece orders Sara to set off a bomb she planted in the building, so that they could die together, but Spencer disbales the bomb, and Emily quickly subdues Sara. Her plans foiled, Cece attempted suicide on the roof, but Alison convinces her to stop, and she declares "Game Over"

Book Series

 * Mona Vanderwaal
 * Alison DiLaurentis
 * Nick Maxwell

Confirmed

 * Mona Vanderwaal
 * Lucas Gottesman
 * Toby Cavanaugh
 * Spencer Hastings
 * Darren Wilden
 * Melissa Hastings
 * Charlotte Drake
 * Sara Harvey
 * Sydney Driscoll
 * Aria Montgomery
 * Jenna Marshall
 * Noel Kahn
 * Uber A

Possible

 * Mary Drake
 * Archer Dunhill

Trivia

 * Big A's identity was revealed to be CeCe Drake.
 * Melissa Hastings and Lucas Gottesman were both revealed to have worked as "A", but both claiming to have been blackmailed.
 * Charlotte and Sara both shared the identity of Red Coat.
 * Sara was the "A" wearing the black veil disguise, which has been nicknamed "The Black Widow" by the writers.
 * Ezra Fitz was believed by the fans and Liars to be Big "A" briefly, before it was revealed that he was instead writing a book on Alison.
 * It is heavily implicated that Mary Drake, Elliott Rollins, Sara Harvey, and Noel Kahn were all working for Uber A at some point. However, only Jenna has been confirmed to be on the Uber A-Team.
 * Shana Fring pretended to be "A" in New York, but was not a member of the A-Team.