AJ Chesterfield is a main protagonist of Total Frat Movie, and the head of the Kappa New Fraternity.
AJ joined Mason Dixon University presumably before Charlie Martin had, and joined and eventually became the leader of Kappa New. During Alpha Chi Gamma's celebration held for their new members including Charlie, Billy and Douche, AJ had his girlfriend Becca and her friend Katie distract the three new Alpha's while he and his frat brothers tampered with Charlie's fireworks. The plan worked, and one of the fireworks ended up smashing through one Alpha Chi's windows and setting the building on fire. AJ successfully caused Alpha Chi to be shut down, framing Charlie for the fire.
Three years later, AJ is still the leader of Kappa New, and is promoting his fraternity during Rush Week. Later during the day, AJ and two of his frat brothers go to or follow Charlie to the abandoned Alpha Chi building, where they find Charlie asleep, and strap him to a chair with duct tape. They tell him within a week, Kappa New will be moving into the former fraternity, and leave, but not before strapping a dildo to Charlie's forehead.
When Charlie, Billy and Douche turn up at Kappa New demanding a duel, AJ refuses, but not before Douche states the 1876 Mason Dixon Duel clause, where if they win a duel with another fraternity, their own will automatically be re-instated. Kappa New is forced to take this duel, and AJ has a fencing match with Billy. Billy wins the duel, leading to AJ walking away screaming.