Mona Vanderwaal is a fictional character in the Pretty Little Liars book series by Sara Shepard, and its ABC Family television series adaption. She is portrayed by Janel Parrish. In the television series, Mona was introduced in the recurring role of Hanna Marin's best friend, and eventually grew into a fan-favorite character after her reveal as the omnipresent antagonist "A". Mona joins forces with a partner in the third season, who eventually takes control away from her. After this Mona forms an alliance with the Liars. In the mid-season finale of Season 5, Mona is seemingly killed by "A". However, in the finale, it is revealed that she is actually alive. Mona was the series' primary antagonist for the first two seasons and the first four books. She was also a major antagonist in the thir