Aaron is a sixteen-year-old graduating senior from Bronxdale Prep in You Know You Love Me. He has his license and skipped 10th grade. He is described as having "a head full of short brown dreadlocks with big brown eyes, pale skin and red lips that curved up in the corners." It is revealed that he has a crush on Blair, but he couldn't tell her because they are step-siblings. He gives up after seeing her with Nate, and he dates Serena for two weeks, although he ultimately breaks up with her after she wears a shirt proclaiming her love for him in a fashion show. He is also portrayed to have a liking for hemp cigarettes, and believes in vegetarianism and global warming.
Aaron is introduced in Pret-a-Poor-J as an upcoming artist about to be featured in Rufus Humphrey's art gallery. While setting up his display at the gallery, he meets Serena van der Woodsen, who is there to see Dan Humphrey. He introduces himself to her, and they start to flirt. Later, Serena goes back to see him and also attends the gallery opening. Afterwards, he asks her to go celebrate the success with him but she turns him down after telling him she isn't dating at the moment. He tells her that if she can figure out the meaning behind Cecil the Caterpillar, he'll go out with her. She's at first confused, then realizes she actually met Aaron years go at Camp Suisse. She explains to Dan that the got "married" with licorice rings, but he "divorced" her when she ate her ring. However, Aaron ends up leaving the opening with another girl on his scooter.
Aaron and Serena keep hanging out, but she keeps becoming put off by the fact that Aaron likes to date more than one person at once (There Might be Blood). However, he tells her he really likes her and they keep casually dating. At Blair Waldorf's 18th birthday party, Serena meets Cyrus Rose; who reveals not only that Aaron is his son, but that he knows he's smitten with Serena. After learning this, she becomes more comfortable with him (Bonfire of the Vanity). Aaron eventually decides to commit to Serena only, and she is thrilled at the news. However, her happiness is short lived when he reveals he is sober. She begins to lie to him that she has never been a partier, but her secret is revealed on Thanksgiving by Dan. After thinking things over, she decides to reveal her past to Aaron. However, he says he doesn't care and that he wants to be with her anyway (The Magnificent Archibalds).
In It's a Wonderful Lie, Aaron's ex Lexi comes to town. She takes an instant liking to Dan, and convinces him to take her as his date to the Snowflake Ball. Meanwhile, Aaron agrees to go with Serena so long as she tries to get along with Lexi. After Bart Bass' death, Aaron goes to the funeral with Serena but feels distant when he sees how close she is with Dan. He invites her to go to Buenos Aires with him over the holidays, and she eventually agrees to go. He attends Cyrus and Eleanor Waldorf's wedding with her and then they leave for Buenos Aires (O Brother, Where Bart Thou?). This is Aaron's last appearance in the series.
In In the Realm of the Basses, Serena reveals to Dan that she broke up with Aaron on the plane, soon after they took off.
- Cyrus Rose (father)
- Eleanor Waldorf (stepmother)
- Blair Waldorf (stepsister)
- Tyler Waldorf (stepbrother)
- Yale Rose (half sister)
- Aaron attended Camp Suisse in Switzerland with Serena. While there, he played a caterpillar named Cecil in a play.
- One of his favorite places is The Cloisters.
- He has a dog named Mookie.
- He is Jewish.
- He likes to date more than one person at a time.