Aaron Stampler is the main villain of the 1996 movie Primal Fear.
In the film
Stampler is introduced as a 19-year-old altar boy for Richard Rushman, the popular Archbishop of Chicago. He appears meek and frightened, with a severe stutter, and alludes to having had an unhappy childhood with his abusive father.
When the Archbishop is brutally murdered, Stampler is found nearby covered in his blood, and is arrested for his murder. Defense attorney Martin Vail takes his case, eager for the publicity. Stampler insists that he is innocent, and that he "lost time" (blacked out) and woke up covered in Rushman's blood. He then says that he often "loses time" when put under great stress.
While investigating the case, Vail finds a videotape of Rushman forcing Stampler, his girlfriend Linda and some of his fellow altar boys to have sex with each other. When Vail confronts him, Stampler flies into a rage and literally becomes like another person; his stutter vanishes and he becomes a violent sociopath who calls himself "Roy". When "Roy" tells him that he killed Rushman after "Aaron" begged him to, Vail realizes that Stampler has multiple personality disorder.
At first, Vail doesn't want to change Stampler's plea, knowing that insanity is hard to prove. However, during the trial Vail goads "Roy" into coming out; "Roy" then attacks and chokes prosecutor Jane Venable until the bailiff drags him out of the courtroom, forcing the judge to declare a mistrial. Stampler is sentenced to a mental institution rather than prison, and Vail becomes the most lawyer in Chicago for helping him beat the murder charge.
When Vail tells Stampler about the judge's decision, Stampler thanks him and asks him to make sure that Venable's neck is all right. Vail realizes that Stampler couldn't have known about Venable's injuries if he had "lost time" as he claimed, and confronts him. Stampler then reveals that the multiple personality disorder had been an act, and that he had known exactly what he was doing when he murdered Rushman; he also says that he killed Linda, as well. Stunned, Vail mutters, "So, there never was a Roy." Stampler replies, "There never was an Aaron, counselor," and brags about having gotten away with murder as a disillusioned Vail walks away.