Mona Vanderwaal (Janel Parrish) is a main character and recurring villainess in the television series Pretty Little Liars and its spin-off, Pretty Little Liars: The Perfectionists, on Freeform.
Mona was a student at Rosewood High School before she graduated and attended Duke University. She was revealed to be the first and original "A" in "UnmAsked" and was sent to Radley Sanitarium for psychological and emotional treatment for several months. Once she received treatment, she was considered emotionally stable and released.
In "Taking This One to the Grave", she was believed to have been murdered and an investigation was launched into her death. It was later revealed that Mona faked her death with the help of "A", who had taken over the game while Mona was in Radley. However, in "Welcome to the Dollhouse", everyone learned that she was alive, having been double-crossed and being held captive in A's dollhouse ever since.
Two-years later, she was later revealed to be Charlotte's Killer. She accidentally killed Charlotte by pushing her against a pipe, however, her reasons for confronting her were to protect the Liars from the game starting up again. She held Mary and Alex Drake hostage in France, in her own dollhouse located in the basement of a doll shop until they escaped. She relocated to Beacon Heights for a fresh start where no one knew her.
Mona was born and raised in Rosewood by her mother, Leona. Mona became friends with Hanna Marin in the 8th grade, and they were great friends. However, when Hanna became part of Alison DiLaurentis' clique in 9th grade, their friendship slowed and eventually ended. Mona was then subjected to intense bullying by Alison, while Hanna and the other girls watched it happen.
Mona never forgot the way Alison had treated her, labeling her as an outsider and a dork. She was even nicknamed "Loser Mona" by Alison and called that by the entire school. She was bullied by Alison, who told everyone she was nothing and treated her like she was invisible. So much so, that Mona herself began to believe it. She resorted to playing with dolls since she didn't many any friends left due to Alison's bullying.
After Alison's disappearance, Mona began behaving like Alison after she assumed Alison's place as the Queen Bee of Rosewood High School. She targeted Hanna, as she figured Hanna wouldn't pass up the opportunity to become popular after having been on the bottom rung of the latter. Mona and Hanna helped each other become skinny and "beautiful" over the summer and became best-friends once again. When they returned to school the following year, they reigned over the students together. Mona taunted Lucas Gottesman in the same way Alison used to torture her, and nicknamed him Hermie, despite once being his friend when Alison bullied them both.
Hanna and Mona's friendship stayed strong until the infamous "A" began torturing the Liars, which forced Hanna to become closer to her old friends. The Liars didn't like Mona, and this is a source of conflict for Hanna and Mona's friendship. Mona turned heel in the Season 2 finale, when she is revealed to be "A", the one torturing, blackmailing, and physically harming Hanna and Hanna's friends. Mona was angry at the Liars for taking Hanna away from her back in 9th grade and bullying her for being different. She was then admitted to Radley Sanitarium where she underwent aggressive therapy to treat her mental health issues.
In Season 3, Mona was a patient at Radley where she was visited by Hanna, Spencer, and Caleb. Unbeknownst to anyone at the time, she was being manipulated by someone wearing a red coat who got her excited to play the game again. When she was released from Radley she attempted to make amends with Hanna, who struggled to forgive her for all the things she did as "A". Mona remained under the influence of red coat until the incident at Thornhill when she was removed from the A-Team.
In Season 5, when Alison is revealed to alive and returning to Rosewood, Mona forms her own army of students and people who were victimized by Alison prior to her disappearance. The goal of the army was to fight against Alison's return and make it clear that Alison wasn't wanted in the town. Her army eventually disbanded and she was able to grow closer to Hanna after framing Alison to be a horrible person. Also during this time, she had an on-and-off again relationship with Mike Montgomery.
In the Season 5 summer finale, Mona found what she believed to be proof of Alison being "A", and was prepared to tell the Liars. She was then believed to be brutally murdered in her own home after the Liars entered the house and saw it torn to shreds.
Due to the amount of blood spread over her home, the police concluded that her wounds must have been fatal and her death was ruled a homicide. In "Welcome to the Dollhouse," Mona was shown to be alive but was held captive by "A", who turned on her after their plan to "kill" Mona. Mona was than forced to pretend to become Alison and her hair was dyed blonde by A. She was also tortured and forced to play games with A. When the Liars escaped the Dollhouse, Mona left Rosewood for several weeks to recuperate from her traumatic experience.
Mona is a very self-conscious person. Due to the bullying and rejection, she faced when Alison was around, Mona developed a complex in which she is not happy with her life. Although she does not show this side of her in public, this is why Mona felt such a need to remain popular, beautiful, and best friends with Hanna. This is also why she started tormenting the girls as "A," because she was afraid that the Liars would steal Hanna from her again, who was her only friend.
Mona is a brilliant young woman who can speak French, hack computers, and do voice impressions. She can be considered a genius but also has a personality disorder, which was diagnosed by Dr. Anne Sullivan.