Question: Who was a at the beginning of pretty little liars?

Disambiguated questions and answers:
context: Original A was the first "A" and revealed to be Mona Vanderwaal. Mona began torturing Alison by sending her gifts, threats and soon attacking her while wearing a zombie costume. "A" continued to mess with Ali and her mother Jessica DiLaurentis, whom she believed it to be Spencer Hastings. After Alison's disappearance, "A" went away for a year but after the corpse of Bethany Young (believed to be Alison at the time) was found, she reemerged. "A" began sending the Liars messages about things only Alison knew about them and soon even began messing with their parents. Doctor Anne Sullivan had previously dealt with the person behind the hoodie and when "A" trashed her office she immediately recognized the person. She almost exposes her identity to the Liars but "A" kidnaps her and went as far as to threaten her son's life. But the Liars are still close to figuring it out and during the second half of season two they manage to get a hold of "A's" phone. They hatch a plan to catch her with this and it works. They find out that "A" had a lair at the Lost woods resort and Spencer and Mona ("A's" newest victim) head over there and find a room full of pictures of Alison and the girls along with a sketch of "A's" costume to the ball, The Black Swan. However, Spencer begins to notice other clues and soon realizes "A" is right there with her. She turns around to see Mona in a black hoodie, who reveals herself as "A". She kidnaps Spencer and gives her an opportunity to join the "A" team but Spencer declines and the two get into a fight, where Mona is pushed off of a cliff. Though Mona survives, she is sent to Radley Sanitarium for medical assistance. While in the psychiatric hospital, Mona takes up a partnership suggested by the then unknown CeCe Drake that starts off the second game. After this, Mona became another henchmen in the "A" hierarchy, obeying the orders of CeCe, whom she knew as Red Coat. Mona was kicked off of the A-Team in the season three finale. However, Mona joins the new "A.D." team in Season 7, after "A.D." sends Wren to kill her and she offers to help instead. She helps them kidnap Spencer and wears a Melissa mask, but ultimately turns on them and brings the Liars to them, as well as a cop. However, this turns out to be a ruse and the "cop" is actually Mona's French boyfriend, who helps her take Mary and Alex (the two remaining members) to France to live in her own personal Dollhouse. Mona is the final "A" of the series, being the "winner" of the game. 
question: Which character was a at the beginning of pretty little liars?
short_answers: Mona Vanderwaal
Mona
wikipage: A (Pretty Little Liars)
context: No context provided
question: Which actress portrayed a at the beginning of pretty little liars?
short_answers: Janel Parrish

Long-form answers:
knowledge: content: "A" is a fictional character in the Pretty Little Liars franchise. Created by author Sara Shepard in 2006, the character serves as the main antagonist in both the television and book series.
wikipage: A (Pretty Little Liars)
long_answer: A is a fictional character in the Pretty Little Liars franchise. Created by author Sara Shepard in 2006, the character serves as the main antagonist in both the television and book series. Original A was the first A and revealed to be Mona Vanderwaal, portrayed by Janel Parrish.