After becoming a major in the Confederate Army, Jasper was set upon by the vampire Maria, who proceeded to turn him. After the transformation, Jasper aided Maria in her creation of a newborn vampire army which successfully conquered the feeding grounds of Texas. However, Jasper became tired of this violent and bloodlust life and eventually became a nomad. Fortunately, he was eventually found by Alice, the love of his life and with her began a life with the peaceful coven of the Cullen family. Jasper Whitlock was the youngest major in the Confederate Army in Texas until he was turned into a vampire by Maria and two other female vampires, Lucy and Nettie, who had recently lost their territory. Maria used him and other newborns to reclaim her place and later claim dominance over others'. Nettie and Lucy were later destroyed by Jasper when they tried to rebel against Maria and take over. Jasper and Maria seemingly shared a short romantic relationship but she never got over her first mate. When he became a vampire, he gained the ability to feel and manipulate people's emotions, which was very useful in controlling the younger newborns. Jasper commanded Maria's newborn army that participated in the Southern vampire wars. Since Maria wouldn't keep vampires that proved useless after their first year, Jasper was responsible to dispose of them, which he did feel remorse for. While in the army, he befriended a newborn named Peter, who Maria decided to keep. When Peter ran off with Charlotte, a newborn that they were supposed to kill, Jasper let them go. After a few years living as nomads in the Northern U.S, Peter and Charlotte came back and told Jasper about the way vampires could coexist in the North, and he left with them. A few years later he left their company, as he was still not happy, since he could feel everything his human victims were feeling while he killed them. He was also reeling from his years with Maria, which had almost turned him into a savage.
Later, he met Alice in a diner in Philadelphia, and fell in love with her. As it turned out, she had been waiting for him. With the help of Alice's 'sight', they searched for Carlisle Cullen and his family. She also told him about the ability to survive off of animal instead of human blood. He didn't know such a thing could exist but he followed her. When he became a member of the Cullen family and while attending high school, Jasper changed his surname of Whitlock to his adoptive sister Rosalie's surname of "Hale" and poses as her twin due to their physical similarities such as hair color. Out of the whole coven, Jasper has the hardest time being around humans, due to his untrained upbringing as a young vampire in an army environment. He was not taught to control or how to regulate his blood lust. He was also the newest member of the Cullen family until Bella and Renesmee came along. In Twilight, Jasper is a senior in Forks High School, along with Rosalie and Emmett. When Edward saves the new girl, Bella Swan, from a car accident with his supernatural strength and speed, Jasper is very upset with his act because he has given away their secret. He later learns to come to terms with Edward's new involvement with Bella when they begin dating, though he needs to constantly keep in distance to stay in control.
During a baseball game, Bella gets unwanted attention from the tracker vampire, James. Jasper assists Alice in taking Bella to Phoenix in order to escape James. While hiding in a hotel room, he senses Bella's guilt of putting them in danger and tries to convince her to not feel guilty, but to no avail. At the airport, Bella takes Jasper to go find a place to eat. Really it was just a ploy to get lost in the crowd and go meet James at her old ballet studio. When they find her, Jasper assists Emmett in ripping James apart and burning the pieces. After James' death and the escape of his mate, Victoria, he returns to Forks and attend the school prom with Alice as his date.
