(Covers information from the D.C. comics)
Dexter Whitlam was an intelligent but introverted teenager who attended Pine Grove Academy.
During his early days as a college student, he was mercilessly bullied by a bigger boy named Kelly and his friends, Todd and Wade. His only reprieve came in the form of occasional help from a fellow student, Ruthie. As a result of his mistreatment, Dexter began developing antisocial behavior, including fantasizing about killing his tormentors, and on one occasion even verbally threatening reprisals.
Dexter's opportunity for revenge came one day when Wade and his friends chased him into the warehouse district. Hiding from the bullies behind a dumpster, Dexter saw men wearing Umbrella Corporation uniforms unloading something from a truck and carrying it into a warehouse. Sometime later, Dexter returned to the warehouse. Within, he discovered a secret lab where Umbrella was conducting G-Virus experiments. In particular, Dexter was awed by the sight of a Tyrant suspended in a large tank of liquid.
When two security guards wandered in and saw him, Dexter impulsively grabbed a syringe containing a sample of the G-Virus and ran. The guards could see he was only a teenager and decided to let him go. Not long after, Dexter analyzed the stolen sample and concluded it was a virus, but unlike anything he had ever before encountered. The sight of the muscular Tyrant made him conclude that the virus would grant him the power he needed to take revenge against the bullies.
Following a particularly vicious beating Dexter finally injected himself with the virus, and immediately transformed into a monster and proceeded to stalk and kill the three bullies. He impaled Wade and shoved Todd's head through a snack machine. He cornered Kelly, who begged for his life, and Ruthie, who happened upon the scene, pleaded with the mutated Dexter not to kill him. Dexter ignored her. He brutally killed Kelly, and would've also killed Ruthie had not two Umbrella agents, who had been tracking Dexter's movements, appeared and one of them stunned the mutated teenager with an electrical gun.
The agents took Dexter to a hospital where after multiple surgeries and treatments, the boy was returned to something resembling his former self. As he lay swathed in bandages, recovering from his ordeal mentally and physically, the senior - Klaus - explained how they were impressed with his ability to figure out what the G-Virus did, as well as by his killing spree, and that they were authorized to offer him employment with Umbrella once he fully recovered.
Dexter simply grinned.
Dexter went under the employment of Umbrella, as offered by Klaus. He was stationed at Umbrella's Arctic Research Facility. He tells the captured S.T.A.R.S. Charlie team member Rosa Cardenas and Patrick Brady about how he impressed he is for their superior combat feats against three animals mutated by the G-virus. He then told the two that they would be perfect for the next X-virus candidates, He begins to do experimentations on them but eventually met his demise when an umbrella surveillance minicopter controlled by Quan Williamson self-destructed, Killing in him the blast radius.