Mona Vanderwaal is a character on Pretty Little Liars. She was the main antagonist of season 1 and season 2, the secondary antagonist of season 3, an anti-hero in season 4, and the main antagonist turned hero in season 5. She is also the main antagonist of the first four books of Pretty Little Liars book series.
Mona was a very intelligent girl who was desired to be friends with the main characters and Alison. They shunned her leading Mona to seek to revenge on the girls. Mona found Alison's diary which contained many of their secrets. She even befriended Hanna to put her scheme into action. Along with Hanna she became one of the most popular girls in school. Mona then adopted the identity of A which she used to blackmail the girls. They thought it was Alison at first but after her body was found they were baffled. Mona then started becoming more vicious in her actions such as outing Emily to her parents and blaming Spencer for Alison's death.
Mona eventually made a mistake when she texted Hanna using her own instead of the one she bought for her plans. This caused Hanna to realize she was A. To prevent her from telling the other girls, Mona ran Hanna over wih her car. Hanna had temporary memory loss because but Mona knew their was a chance Hanna could regain her memories. Mona then sent herself text messages from A to throw suspicion off of her. Mona later tricked Spencer into getting into a car with her by telling her they were going to the police station. Hanna regained her memory and texted Spencer warning her of the danger. Spencer tried to escape but Mona realized this preventing her from doing so. They headed into a deserted area of Rosewood where Mona told Spencer she was A explaining she did it because she had been shunned by the girls so she wanted revenge on them. Another part of it was because she had seen them accidentally blind Jenna with a firework.
Mona told her she knew their secrets from Alison's diary and asked Spencer to be A with her. Spencer refused causing Mona to start choking her. Spencer then killed Mona in self defense by pushing Mona to her death.
Mona's role in the television series is very similar to the books until the end of Season 2. Instead of dying, she ended up being locked up in an insane asylum. Mona was visited by somebody in a red coat telling them she had did everything that they wanted. Hanna started visiting Mona in the asylum but her Mona showed no signs of recognition at first before Hanna gave her a make-over. The next time Hanna visited her, Mona asked about the new A and later Caleb visited Mona warning her to not mess with Hanna. Later, Mona managed to sneak out of the asylum dressed as a nurse where met up with another member of the A team revealed to be Toby.
Mona told him she was disappointed that their plans had not worked out. During Halloween, Mona snuck out of the asylum again and wore the same costume as Caleb. This fooled Hanna until she saw the mask on that Mona made to her her identity. She apparently made her way back to the asylum pretending to be asleep when a nurse checked on her.
- Mona was arguably an anti-villain in seasons 1 and 2, because her actions against the Liars, while sometimes extreme, were somewhat understandable and justifiable considering the way she was treated by them.