Alison DiLaurentis

Alison DiLaurentis is a main character in the series and the best friend of Hanna, Aria, Spencer, and Emily. In the television series she was the Queen Bee of Rosewood High School, before mysteriously disappearing only to be found dead one year later. In the book series, her life is stolen by her twin sister Courtney and is sent to a mental hospital in Courtney's place before returning to kill Courtney and regain her old life back.

She is portrayed by Sasha Pieterse

Physical Appearance
In the book, Alison is described as beautiful, with a heart-shaped face framed by long blond waves and big blue eyes.

Book Series
Alison (Ali) DiLaurentis is the most popular girl at Rosewood Day. She has a secret identical twin, Courtney DiLaurentis - who she hates. Alison's best friends are Naomi and Riley, who she describes as the 'coolest girls in school'. Alison holds commanding reign over her year, everyone envies her and is interested in her. During 6th Grade, Ali spots a flyer for the Time Capsule Tradition, and announces that she will have a flag given to her by her brother Jason DiLaurentis. Ali's signature 'A for Ali' ring was stolen by her sister Courtney. That night Hanna, Aria, Spencer and Emily arrive at Ali's house to steal her flag piece but Ali tells them that someones already beaten them to it, only it isn't Ali talking to them. It's Courtney who is about to swap mental hospitals, wearing Ali's signature ring. Instead of Courtney being taken back to the hospital it is Ali as Courtney tricked her parents into believing that she was Ali. Ali insists to her parents she is Courtney, but without her ring her parents don't believe her and just think that it is Courtney becoming more crazy. Furious, Ali realizes the only way out is to pretend that she is Courtney, eventually her parents let her out for a break the next summer. Ali becomes obsessed with stealing her life back. Courtney has befriended who Ali thinks are the 'un-cool' people of Rosewood Day - Hanna, Aria, Spencer and Emily. While they are having a sleepover with 'Ali' in Spencer's barn Ali spies on them, taking pictures with a polaroid camera, eventually she ditches the photos in the woods behind her house. When Courtney runs into the woods after an argument with Spencer, Ali confronts Courtney and eventually kills her by shoving her into a hole where a gazebo was about to be constructed in their backyard, afterwards Ali ran back up to her bedroom. Ali was sent back to the mental hospital, because her parents didn't want her to be fussed over by the media who had become involved in disappearance. Whilst in the mental hospital, Alison befriends a girl called Iris. Eventually Allison takes over from Mona and becomes 'A' to continue to stalk the PLL's and keep herself hidden at all costs, including killing Ian Thomas who knew about Alison's existence. this eventually turns into a near murder, when Alison starts a bush fire to burn down Spencer's barn and kill the PLL's inside. Only Alison is trapped by a fallen branch and is nearly killed herself, Aria finds her and rescues her. The rest of the PLL's see her, but Alison runs away before her identity is revealed. Alison also kills Jenna in the book Heartless as Jenna also knew about her existence. Alison returns in Wanted, when her parents, who still think she is Courtney introduce her to the rest of Rosewood, saying that she was 'Alison's' twin, and they didn't want her in the spotlight. Alison convinces the rest of the PLL's that she is Courtney, which they knew as Alison. They become friends again, and they all think that it's just like old times. Alison invites them to a holiday home they had always used to visit with Courtney and Alison makes them re-inact the scene of then night Courtney was murdered. Alison planned the night so she could blow up the house, killing the PLL's and finishing what she started. Only again, she fails the PLL's escape the house and seemingly Alison is trapped inside and thought killed. At the end of the book, a new girl starts her senior year at an anonymous school, a girl whose name just so happens to be an anagram of Alison DiLaurentis...

Television Series
In the series, Alison is portrayed by Sasha Pieterse. Much like in the book, Alison is the most beautiful and popular girl in Rosewood, and is the envy of many. She surprisingly befriends Hanna, Aria, Spencer and Emily who previously considered themselves un-cool, together they become the most popular girls in school sharing sleep-overs, pool parties and shopping trips with each other. Ali knows each of the girls' biggest secrets and constantly teases them or hints about them in conversations. In the summer after 7th Grade, Ali holds a sleepover in Spencer's barn with her best friends Spencer, Hanna, Emily and Aria. She convinces them to let her hypnotize them, only Spencer disagrees and the two get into a heated argument outside, which ends up with Ali running into the woods and meeting someone by the kissing rock. She goes missing, presumed dead and for a year her body is never found. The new owners of the DiLaurentis's house (who moved away after Ali vanished) decide to get rid of the Gazebo in the backyard and construction workers discover Ali's remains in the ground below it.

Friends
In the TV Series, Alison is the ring-leader of her group of friends, which consists of Hanna, Aria, Spencer, and Emily. Alison disliked Mona Vanderwaal, who her friends constantly made fun of. Alison treats Hanna like her lackey and Emily is hinted to be more than a friend.

In the book, Alison's main friends are Naomi and Riley. When Alison is forced to become Courtney, she befriends a girl called Iris. After being released from the clinic, Alison becomes friends with Kate, Naomi and Riley, who all think she is Courtney. To the PLLs, she reveals herself as Ali and pretends to be the Ali they knew. It is revealed later that she only became "friends" with them in order to kill them.