Aubrey Posen is the main antagonist of Pitch Perfect. She is the leader of the Barden Bellas and one of the protagonists of the film, though despite this, she is very hostile towards the Bellas and wants to win at all costs, sometimes bringing her to cross the line between hero and villain. Near the end, she and the girls have a heart to heart and she becomes full on hero from here on out.
However, she returns to anti-hero/antagonist status in the sequel. Though this time it's more friendly hostility than all out antagonism.
She is portrayed by Anna Camp, who also portrays Sarah Newlin.