A (Book Character)

The book series
"A" in the book series is an anonymous character who sends threatening texts to the girls, revealing secrets that they thought no-one knew, or only Alison knew. Each of the Pretty Little Liars receive texts and don't know that the others are getting them as well, as they keep them to themselves in fear of their secrets being revealed. Each of them believe that Alison is somehow alive or dead, sending the texts from beyond her grave for revenge. Only when Alison's body is discovered do they open up to each other about the texts and realize that the sender isn't Alison. They later find out it was Hanna's friend Mona, but after she died a new "A" took her place.