Mona Vanderwaal

"It's easier to forgive an enemy than it is to forgive a friend."

- Mona Vanderwaal

"Game Over, Ali, and I win..."

- Mona's last words before her alleged "death"

Mona Vanderwaal is a character on Pretty Little Liars. She was the hidden main antagonist of seasons 1 and 2, the true secondary antagonist of season 3, an anti-hero in season 4, the initial main antagonist turned heroine in season 5, and an anti-heroine/antagonist in season 6 and a major antagonist in season 7. She is also the main antagonist of the first four books of Pretty Little Liars book series.

Mona is revealed to be the first and original "A" in both the television and book series, and was anonymously stalking and blackmailing the liars until her identity was revealed in the Season 2 finale in the TV series. It is also revealed that Mona is responsible for the death of Bethany Young, as she bludgeoned to unconsciousness (thinking she was Alison DiLaurentis), leading to Melissa Hastings burying her alive, killing her. In the book series, she falls to her death after her reveal, however in the television series, she survives and continues being "A" before eventually becoming an anti-hero.

Mona is also revealed to be the person who murdered CeCe Drake, although she claims it was self-defense.

Book series
Mona was a very intelligent girl who 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, framing Spencer for Alison's death, burglarizing the Liars homes, and threatening to harm Dr. Sullivan's son, forcing her to flee the city.

Mona eventually made a mistake when she texted Hanna using her own phone 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 with her car. Hanna had temporary memory loss but Mona knew there 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 and prevented 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 off a cliff to her death.

Television series
Mona's role in the television series is very similar to the books until the end of Season 2. Instead of dying from her fall off the cliff, she ended up being locked up in an insane asylum. In the psych ward, Mona is sadistically unrepentant and satisfied that the Liars will feel safe with "A" incarcerated, as they don't know she was part of a conspiracy, and that a false sense of security is exactly what "they" want.

Mona was visited by somebody in a red coat. Mona told them she had did everything that they asked her to. 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.

When she returns to school, the student body is aware that she is a psychopath, and avoid her. However, she plays the victim and succeeds in winning them back, although the Liars are still wary of her because someone tried to hit Lucas with a car after he cut ties with Mona, likely someone working for Mona, if not Mona herself. (This person was later revealed to be Toby.) Mona also causes Meredith Sorenson to be harmed in an explosion, and makes it appear as though the Liars were responsible.

To torment Spencer into joining the A-Team, Mona steals her spot as captain of the decathlon team, as a spot was open on the team because one of the members was injured in a bike crash, because Mona tampered with his bicycle. She also has Toby fake his death, driving Spencer further insane, and she agrees to become A, as she had refused before. However, Mona sides with the Liars in the Season 3 finale after she is almost killed in a fire because of Red Coat.

Mona returns to her conniving ways in Season 5 when she begins building an army to prevent Alison's return to Rosewood. When this fails, she fakes her death and frames Alison for murdering her. However, while she was "dead," Charlotte DiLaurentis kidnaps her and holds her hostage in a doll-house. Mona later escapes with the help of the Liars, and shortly afterwards kills Charlotte, supposedly out of self-defense. She also reveals that she killed Bethany years earlier. She spends the remainder of the season avoiding Uber A's attempts to avenge Charlotte's death.

Trivia

 * She is portrayed by Janell Parrish.
 * Mona is arguably the "bigger bad" to Alison in the books since she is the one who began the game in the first place.
 * In the book series, Mona never murdered or killed anyone, however in the television series, she killed two people.
 * Mona was an outsider who was bullied by Alison and wanted to be friends with her, which is what drove her to become "A".
 * She started the "A" game just to harass Alison for her bullying and began it again to prevent the Liars and Hanna from becoming friends again.
 * She became somewhat reformed in season 4 after being kicked off the "A"-Team. In season 5, she started out as the main antagonist before becoming an anti-hero again, which she remains today.
 * She also become a reformed mean girl in seasons 5 and 6.
 * She was similar to Rachel Gatina from One Tree Hill, an outsider and a geek. She had a million dollar makeover that transformed her into a mean girl.
 * Mona was revealed to be the person who hit Bethany Young with a shovel, mistaking her for Alison from behind because they were wearing the same outfit and had the same hair color (blonde). She claimed to have hit her because she was upset over everything she did to her, saying she "could hear every awful thing she said all at once" when she hit her. Bethany was then later buried by Melissa Hastings.
 * Mona appears to be slightly masochistic, as seen in Season Three, when she intentionally made herself bleed with a pair of tweezers.
 * Mona supposedly died in the twelfth episode of the fifth season, titled "Taking This One to the Grave". She was attacked by Big "A" before the Liars found blood all over the walls in her house. Her "corpse" was shown at the end of the episode, but it was revealed that "A" had drugged her with something that caused her to not move and look like as if she was dead. The blood found in the house was a result of her drawing blood from herself since she was originally planning to fake her own death. "A" was holding her captive for several months, though she eventually escaped.
 * Mona is a unique character in that for the TV show she starts off as the Big Bad for the first two seasons, becomes a henchmen in the third season, while also being somewhat of a Bigger Bad since the "A" idea was hers, then becomes an anti-hero in season 4, initially a Big Bad again in season 5 before becoming an anti-hero once more and is currently an anti-hero.
 * In the book, Mona was motivated in part by a desire to avenge Jenna's blinding. In the series she possesses no such motive and is in fact Jenna's rival for Noel Kahn's affection.