Mona Vanderwaal (Janel Parrish) (season 1 -- 7) is a former unpopular girl at Rosewood who longed to be accepted into Alison 's group and was continuously mocked by Alison. After Alison 's disappearance, Mona befriended Hanna and they underwent an "extreme makeover '' together; as a result, they both became popular students. When "A '' appears, Mona becomes jealous of Hanna rekindling her friendships with the other Liars. She dislikes Caleb and makes attempts to break Hanna and Caleb up, though to no avail. She becomes romantically involved with Noel, much to Hanna 's disapproval, but is later dumped by him for Jenna. When "A '' begins sending Mona threatening notes, she grows closer to the Liars. In the second - season finale, she is in fact revealed to actually be "A '' when she and Spencer travel to the Lost Woods Resort to uncover "A '' 's lair. She is committed to a mental institution, Radley, after being diagnosed with borderline personality disorder. Here, someone known as Big A takes the "A '' game away from Mona and starts an "A-Team '', consisting of Mona, Toby, Spencer, Melissa, Wilden, and Lucas. At Radley, Mona gives answers to Hanna concerning Maya 's death. Possibly unbeknownst to Big "A '', she secretly gives Maya 's website to Hanna in code, leading them to eventually discover that Nate killed Maya. Mona reveals that a person in a red coat came along and changed the game, becoming the new "A ''. Mona later reveals she actually does n't know who "Red Coat '' is, and is basically expelled off the team for letting Spencer and Toby trick her. At the end of season three, Mona gets a text along with the rest of the girls in red font: You 're mine now. Kisses! - A, implying she is now a victim of "A ''. Mona begins helping Ezra with his book in 4B due to him blackmailing her because of her illegal "A '' activities. In the season 4 finale, Alison reveals that Mona helped her the night she was hit over the head and convinced her to go into hiding. In Season 5, she starts an army of Alison haters to prepare for Ali 's return. The team consists of Lucas, Melissa, Jenna, Sydney, and various other people that were treated badly by Alison. In the season five mid season finale, she is killed by Big "A '' after acquiring information that proves Alison is Big "A ''. In the second half of the season, it is revealed that Mona never thought Alison was Big "A '' and instead, it was a plot by her and Big "A '' to get Alison into jail. Mona was to fake her death as part of this plan, so that she could find out Big "A 's '' identity, and in the fifth - season finale it was revealed that Mona is really alive and being forced to "be '' Alison inside Big "A '' 's Dollhouse. She escapes the Dollhouse with the other girls in season six, and ends up finding out Big "A 's '' true identity to be CeCe Drake, alongside the others. During this revelation, Mona realizes that she was the one who hit Bethany Young with a shovel that night, believing she hit Alison, but discovering the truth once CeCe reveals that it was her who hit Alison.
who plays the character a in pretty little liars
Janel Parrish