Jason DiLaurentis

Jason DiLaurentis is Alison DiLaurentis' elder brother. He was an Emo/Punk a few years before the events in the present day. He admits to having been a substance abuser before turning his life around, graduating from an Ivy League institution and picking up more wholesome hobbies, such as long distance biking and photography.

History

Early Life
In "If At First You Don't Succeed, Lie, Lie Again" it is revealed he used to smoke pot, and hang out with Ian Thomas during the summer a couple of years ago. It was also revealed in a flashback in Season Two, that he almost hated Alison because she would often go into his room and take his belongings. Jason later reveals that he was jealous of Alison, and had felt that his parents thought they "lost the wrong kid"

Season One
He came back in "Please Do Talk About Me When I'm Gone" with a new clean cut look that surprised most of the girls. His purpose in returning to Rosewood was to help organize Alison's memorial. (This turned into his directing the project.) He is now guarded and keeps secrets. Jason reveals to Spencer what Alison also told him about "The Jenna Thing," specifically her revision in which Spencer was behind everything, including being the one to throw the stink bomb. When he talks about it with Spencer, she asks if he believes his sister's story; he does not reply back, making her say that he's just like his sister. To this he replies saying he's even worse than Alison. The day after the memorial, he decides to give the girls Alison's bracelet and leaves.

Season Two
Jason returns once again, however Parker Bagley has been replaced by Drew Van Acker in order to make his appearance similar to the Jason from the book series. He moves into his old house, in which he once lived with his sister, Alison, after receiving money from an endowment. Spencer visits him and offers to help him move in properly, however he declines her help and questions Spencer about Alison's death, asking whether Ian really admitted to killing her. Jason seems dissatisfied with Spencer's vague answer.

At the end of "The Goodbye Look," Jason is building a fence around his home, from which he want to keep people out, however the liars seem to think to keep someone in, more specifically, Ian. He eventually hires Toby Cavanaugh to help him with the construction work when he was fired from his previous job. Jason holds onto the fact that he is the only one living in the house, but Spencer did see a figure in Jason's window while Jason was outside. However, there is no proof it is actually Ian, and Ian's body being found in an old barn later confirms this.

In "The Devil You Know," it's learned that Jason was always very Jealous of Alison, and he feels he should of died instead of his sister. Jason confides to Aria that it is possible that he killed Alison, as he has no recollection of what happened that night, but knows that he could be violent when jealous. Jason shows Aria a piece of paper he received the next day, warning him that someone knew what he did, though the reference is vague. That slip always made him worry that he might have been the one to harm Alison. However he admits the relief he feels from the closure that Ian's confession had brought him.

From "Blind Dates," it is shown that Jason has feelings for Aria, telling her that he missed the pink hair, or not calling the cops when Mike wanted to rob his house and having sort of a moment when he brought Mike back to the Montgomery's home.

In "Never Letting Go," Noel shows up with a CD that he claims could theoretically incriminate Aria and the rest of her friends; Jason steps in, takes the CD, and snaps it, not allowing Noel to bully Aria. He then offers Aria a ride home, and she accepts. Jason seems oblivious to the fact that Aria is romantically involved with Ezra.

Aria/Jason/Ezra Love Triangle
Jason's character is developed to a great extent in "Surface Tension". He visits Rosewood High on a school day to talk to the guidance counselor; he wants to help at-risk high school students by showing them that there is light after high school. Aria finds Jason sitting in Ella's classroom after his meeting before Ella lets Aria know that Jason is also invited to dinner that night, and Aria gives him a half-smile. Ella has invited Jason, realizing that he could use a break from his own family and also as a thoughtful gesture towards Jessica.

Later at school, Aria lets Spencer know that Jason is set to come over, in addition to Ezra. Spencer is alarmed as she doesn't trust Jason, but Aria is worried for the reason that it will be awkward.

That night, Jason arrives at the Montgomery household with flowers, which he hands them to Aria. Jason and Ezra meet for the first time. Aria steps out of the party to answer a call from Spencer, warning Aria that Jason may have been involved in Ali's death and to be alert with Jason in her house. Knowing that the hockey stick was right on the property line and that Jason was moving the property line so as to include part of the Hastings' property, Spencer finds it awfully incriminating. She finds it doubly incriminating that Jason doesn't remember anything from the night Ali disappeared. Making Jason look even more worse is Aria's flashback of Jason the day that Spencer was showing Ali how to hold the hockey stick. He had come looking for her on their mother's orders, unhappy to have to find Ali. He had grabbed the stick from her and then threatened to hit her with it. After that, Ali had tried to whack her brother with the stick, but Jason had moved quickly and mockingly warned Ali that she wouldn't get a second chance.

Later, back at the party, Jason and Ezra get to know one another, sharing their stories about their hard-core biking. Then, Officer Barry arrives to inform them that Mike has been caught breaking into a house, totally breaking up the dynamic of the dinner party. Jason and Aria exchange knowing looks, at which Ezra raises an eyebrow. Byron and Ella leave to pick him up, leaving Ezra, Jason, and Aria alone in the house. The two guys help Aria put the serving plates away. In the kitchen, Ezra questions Aria about Jason, asking who he is. She answers that he is Ali's brother, to which Ezra responds that he knows, clearly expecting a more specific answer. Aria goes back out to the living room, where Jason is sitting, under the guise of wanting to offer him coffee. But Ezra isn't oblivious to the fact that the two are whispering privately. Aria and Jason discuss Mike's arrest; she lets him know that Mike had promised her that he wouldn't repeat his mistake, and he wisely lets her know that he probably meant it at the time. He also tells her that if this is his first time getting caught, he has probably raided multiple houses before. After Aria finds Jenna's pottery piece in Mike's room, she rushes down the stairs, suddenly telling Ezra and Jason to leave. So they leave, pausing briefly at the doorstop for an awkward stare-down before going their separate ways.

In "Picture This," Jason tries to pursue Aria and kisses her. She tells him she isn't available and leaves him. Spencer and Emily find out that Jason had been stalking Aria and taking pictures of her without her knowing, suspecting that some of them were taken while Aria was asleep. When Emily and Spencer go back to Jason's shed hoping to procure picture evidence for Aria, all of the pictures are missing.

Trivia

 * Jason has longer, blonde hair in the books.
 * Parker Bagley portrayed Jason through Season One of Pretty Little Liars, however in Season Two he was replaced by Drew Van Acker in order to make his appearance more similar to the one of Jason from the book series. Drew Van Acker is also arguably more attractive than his predecessor.