It was one of the longest-running mysteries on Pretty Little Liars, so who was the twisted stalker known as "A?" Pretty Little Liars is a based off a series of books by author Sara Shepard and follows a group of teen girls who have to learn the identity of "A," who threatens to reveal their darkest secrets and punish them for past mistakes. They first believe it could be their friend Alison, who vanished a year prior, but when she later turns up dead, things take a progressively darker turn.
Pretty Little Liars was met with mixed reviews throughout its seven-season run, though it always maintained a loyal audience following. While the premise leaned close to movies like I Know What You Did Last Summer and Heathers, the show's blend of teen drama, dark comedy, and thriller made it a hit. It also spawned spinoff shows like Pretty Little Liars: The Perfectionists and supernatural series Ravenwood, which lasted one season.
Of course, Pretty Little Liars eventually had to reveal the identity of "A," and whilst others characters would don the mantle in later series, the original "A" was revealed to be Mona Vanderwaal, played by Janel Parrish (To All The Boys I've Loved Before). Mona states her reasons for taking on this alias was due to bullying from former clique leader Alison, who refused to let her be part of their group. Mona eventually became popular following Alison's disappearance but sought revenge against the girls for their past actions.
Mona is revealed to be "A" in Pretty Little Liar's season two finale "UnmAsked," and after getting into a vicious fight with Spencer (Troian Bellisario), she's committed to an Asylum and diagnosed with multiple personality disorder. In season 3, Mona teams up with other characters to form The "A" Team, but when she later becomes a victim of the group herself she has to join the Liars for help. A villain dubbed "A.D." would later make their lives hell again in the final two seasons of the show.
Mona is commonly considered the best character on Pretty Little Liars and she later returned for sequel series Pretty Little Liars: The Perfectionists in 2019. "A" made for a formidable villain in the early seasons and Mona continued to be a complex character throughout the series, with her allegiances shifting back and forth throughout. While there were many pretenders to Mona's crown following season 2, in the series finale she proved she was still the best by defeating "A.D."