Jessica DiLaurentis is one of the main antagonists from Pretty Little Liars. She is at first presented as the sweet, damaged mother of Alison; however, it is soon revealed that she has dark secrets of her own and is in an agreement with "A". She is the main antagonist for the final episodes of Season 4 and a "Big Bad" for most other seasons.
According to the executive producer and main story writer of the show, I. Marlene King, Jessica is the true villain of the story.
Known for her controlling ways, Jessica buried alive Alison, her daughter, after she thought Charlotte DiLaurentis had unknowingly killed her with a rock to the head. After that, she tried to frame Spencer Hastings for the murder. Although Alison was found to be alive, Jessica was soon murdered by an unknown assailant and buried in the Hastings backyard by villainous "A".
It was revealed that Jessica was the "evil twin" and Mary was the "good twin" in "Original G'A'ngsters" and that Jessica often had Mary tortured when she was in Radley Sanitarium.