Aria Montgomery

Aria Montgomery is one of the main protagonists of the Freeform series Pretty Little Liars. However, in the series' seventh season, Aria becomes a supporting antagonist.

Aria is one of the Liars, the group of girls being tormented by "A". However, when Uber A takes over, they offer Aria the chance to join the A|A-Team, in exchange for them protecting her secret. She accepts and becomes "A.D.'s" helper.

Season 7
Power Play

Aria receives a video chat from "A.D.", claiming to have intel in her file that could ruin her relationship with her fiancée, Ezra. "A.D." video chats with her again and tells her to meet them. She goes to the location and sees a limo. The door opens and she enters to see "A.D." sitting there. They reveal themselves as Sydney Driscoll, who quickly admits to shooting Spencer, rescuing Jenna from the blind school, and creating the board game. She offers Aria the chance to join the A-Team and Aria realizes she is wearing an earpiece and the driver of the limo is the real "A.D.", prompting Aria to confront Sydney. Sydney reveals that Aria has a long way to go to prove herself to "A.D." and they leave Aria at an unknown location.

At the end of the episode, "A.D." asks Aria, via text message, if she has made a decision yet.

In the Eye Abides the Heart

Aria finally accepts "A.D.'s" offer, giving in to their threats. She is tasked with giving them information on the Liars, and then delivers them Lucas's comic book. In return, she is given a black "A" hoodie.

Trivia

 * Aria being "A" or on the A-Team has been a hugely popular theory amongst the fandom since the show's beginning.