Pretty Little Liars book fans, beware! Even you’ll be surprised to find out who “A” is on TV. Sadly we don’t know “A’s” identity, not even the PLL stars do, but we can tell you that “A” WON’T be the same person as in the books. The writers had to create a new “A” because there would be little mystery if they didn’t switch things up.
"A" was several people throughout Sara Shepard's series, but she started off as Mona (Janel Parrish). But, the little liars eventually realized this and Mona died in an accident. But don't worry, knowing this won't ruin the show says Lucy Hale (Aria). She told MTV, "In the books, it's Hanna's best friend [Mona], but we're doing it completely different on the show."
However, if you want further proof that "A" will be someone different on TV, who better to turn to than PLL Executive Producer Marlene King? She explained to TVDoneWright that they needed to change "A" in order to continue the show and keep fans in suspense. “We can’t stay completely true to them [the books] or we would have been over in 8 episodes. We slow down the stories, twist and turn their plots but always stay true to the characters, tone and the world Sara created.”
Those who’ve read all eight books know that after Mona died, there was a shocking ending involving Alison’s troubled twin sister, Courtney. Courtney spent her life in institutions, but when she came home the summer after seventh grade, she pretended to be Alison and her parents believed her. They then sent the real Alison back to the institution, which means Courtney (as Ali) was killed during the barn sleepover. Alison was angry that Courtney stole her life, so after Courtney died, the real Alison took revenge as "A." Judging by everyone’s explanations that “A” won’t be the same as in the books, we’d say the whole twin impersonation twist probably won’t happen on TV.
Sources: MTV, TVDoneWright