Alexandra “Alex” Drake is a fictional character created by I. Marlene King and portrayed by Troian Bellisario in the American television series Pretty Little Liars. Officially introduced in the series finale, Alex Drake is both the identical twin of main character Spencer Hastings and the previously anonymous identity known as "A.D." In childhood, Drake was adopted by a wealthy British family that later abandoned her, forcing Alex to bounce around foster homes and orphanages. Because of this, Alex would frequently impersonate Spencer in adulthood due to jealousy over her happier upbringing. Alex Drake is considered the deadliest antagonist of the series. As "A.D.", she blackmailed, stalked and tortured the main characters in an attempt to discover Charlotte Drake's murderer. The character's twin storyline pays tribute to Alison and Courtney DiLaurentis, characters of the Pretty Little Liars book series. Development Bellisario was cast as Spencer Hastings, in November 2009. Alex is Spencer's identical twin sister, whose existence was unknown until the series' final episode. During an interview to Elle, Bellisario disclosed that Marlene King, the show's creator, was planning to introduce Spencer's twin since 2014, when the show's fifth season began airing. She also commented that King was initially doubtful towards the storyline since Freeform wasn't decided if the show was going further forward. However, by the end of the sixth season, Marlene warned Bellisario they were staying true to the plan, so they began working on the character's history and characteristics. According to Bellisario, the difference between Alex and Spencer is that "Spencer approaches things with her head and her heart, and Alex approaches things with her head and her groin. That's not to say she doesn't have a heart or feelings, but she's gotten really good at putting a thick coat of armor over her heart." Referred to as the series' "ultimate villain," Alex is an "Essex girl" whose portrayal was influenced by late singer Sid Vicious. She is a manipulative woman who can easily disguise and pass herself off as Spencer. Alex is desperate to take over her twin sister's life since Spencer has a supportive cycle of friends and family, while Alex was twice abandoned and forced to live on her own terms. Storylines Background Alex is the third and last child born to Mary Drake after Mary posed as her twin sister Jessica DiLaurentis to sleep with Peter Hastings whom Jessica previously had an affair with.