Alison Lauren "Ali" DiLaurentis is a fictional character in the Pretty Little Liars book series by Sara Shepard, and in the ABC Family television series adaption. She is portrayed by Sasha Pieterse in the television series.Throughout the first three seasons of the television series, Ali mostly appears in flash backs and hallucinations. The character of Ali plays a more prominent role from season 4 onwards. Alison has an alter ego named "Vivian Darkbloom" whom she uses to spy on "A."