"A" is the main antagonist of the series. A is an extortionist who is privy to the Liars' deepest and darkest secrets and uses these secrets to exact revenge on the Liars for (often) perceived wrongdoings. The first "A," Mona Vanderwaal, was able to discover the Liars' secrets by reading Alison's old journal. During a physical confrontation with Spencer Hastings, Mona was pushed over the edge of a quarry and fell to her death. The second "A" was Alison DiLaurentis, who killed Courtney DiLaurentis, Jenna Cavanaugh, and Ian Thomas. She also attempted to kill the Liars and Spencer's sister, Melissa. Alison is presumed dead after being caught in a house fire. After accidentally killing a girl while on vacation in Jamaica, a new "A" appears.
Alison DiLaurentis was an extremely popular and cruel girl who went missing three years prior to the beginning of the series. Her body was finally discovered buried under the gazebo on her family's former property, launching a murder investigation. She befriended the Liars near the end of sixth grade and, over time, was able to learn all of the Liars' most personal secrets, something that she often used against the Liars in order to keep them...