Sean Miller was high school kid who was also a thrill-seeking sociopath.
Sean Miller was a student at Hamilton Hill High School, where he shared a history class with Terry McGinnis and Max Gibson. Sean was a typical delinquent who seemed to find pleasure in his vile actions as well as a disregard for human life. After a joyride in a cargo truck, his parents sent him to Dr. Wheeler's clinic.
Shortly after, he welcomed Chelsea Cunningham into the clinic, where he served as her guide. Through this he also revealed a severe paranoid side to himself, accusing her of talking about him behind his back. When Terry came to "visit", Sean picked a fight with him. Unfortunately, Vincent broke them up and Wheeler sent him to ISO. The next morning, as Sean and Terry were transported to the ISO rooms, they started a revolt. Sean freed as many of the other kids as he could, but they were overrun by guards using tear gas and cattle prods.
Sean snuck away from the fight and went in search of Wheeler. He attempted to kill him by pushing him off the roof. Batman tried to persuade him to let Wheeler go but he refused and pushed Wheeler off, forcing Batman to rescue him. Wheeler was arrested and the clinic was shut down. Unfortunately, for his attempted murder, Sean was arrested too.