Molly...she's the kind of person who fries ants with a magnifying glass just to watch them flail around.
-Christina on Molly
Molly Atwood is one of Peter Hayes's lackeys along with Drew. All three of them come from Candor. She was Tris Prior's enemy during the Dauntless initiates and she tends to mock her and her friends whenever she has the opportunity.
Molly is almost always with Drew and Peter, or at least where it is mentioned by Tris. She constantly mocks Tris, like the time when she helped Peter and Drew humiliate Tris by ripping away Tris's towel, exposing her. In stage one, she fights with Christina and beats her easily, but then she fights with Tris. Tris, angry at her, knocks her down. She kicks her in the head, the chest, and the stomach from rage. Molly's face is covered in blood by the time Tris is done with her. Tris was carried away from her by Four while she's bleeding. Tris is asked if she needs to take a walk to calm down, to which she replies that she is fine and knows she should feel a little guilt for beating her, but doesn't. However, Tris does feel bad about it after Eric compliments her. Molly's rank then becomes lower than Christina's and because she failed to a weak opponent (Tris), she stated that Tris would "pay for this". She made an Erudite reporter write a cruel article about Tris's dad, on "how Tris Prior had a cruel upbringing". Molly lied about Tris's father infuriating Tris.
However, in the film, there is no record of Molly specifically feeding the Erudite reporter the false information. Instead, when Tris volunteers to stand in front of the target instead of Albert during training, Molly is seen complimenting her, stating that Tris' actions were "cool". In the film she is shown to beat Tris in their fight lowering Tris' ranking because Eric paired the 'first jumper', Tris, and the 'last jumper' which is Molly.
Later, because of her low rank, she becomes factionless and probably goes wandering the streets of Chicago along with Drew.
In Insurgent, it is pointed out that Molly and Drew tried to join the division of the factionless that Edward and Myra were in, but because Edward was "upset" by Peter, he didn't let them join. It is also mentioned that Drew was very badly beaten up by Edward.
Molly is described as strong, broad-shouldered, tall, large-bulked with dark apathetic eyes, she's shorter than Peter, but taller than Christina and is muscular in arms. She has bronze skin and also has a large, 'bulbous' nose. According to Tris, her teeth are very crooked and angular. She is described as being unattractive. Much like her appearance, Molly has an ugly laugh, which consists of snorting and shaking.
Molly bullies the other initiates, and shows extreme dislike for Tris. Molly is also very cruel and rough. She is very proud and gets jealous when other people are better than her, but in the film it is shown that Molly does have a kind(ish) side. Also in the book Molly is shown to be complimenting Tris, although this is rare. Throughout the story, Molly has never been a leader, she is more of a follower. She follows Peter and does everything he says.
Molly's parents do not visit her on Visiting Day, which might hint to a troubled home life. This could also explain why she has a harsh and brutal personality.
Peter and Drew
Molly, Peter, and Drew have been childhood friends since birth, and have often worked together.
For unknown reasons, Molly is not one of the attackers who tries to murder Tris by throwing her over the chasm.
Like Peter, Molly seems to show a disliking towards Tris. She teased her by calling her a child. This made Tris angry, so she beat Molly in her final fight.