John Mostow

John Mostow was one of the main villains of the X-Files episode "Grotesque" - alongside Bill Patterson and the Gargoyle : he follows a trend in the show of serial-killers with paranormal powers, though unlike many of the other villains in the series Mostow is shown to be deeply disturbed and does not wish to inflict death on others, blaming his actions entirely on the Gargoyle.

History
John Mostow is a man apparently suffering severe mental illness that manifests in his art, causing him to draw gruesome imagery of a gargoyle - which he claims to be a demon that is possessing him.

Despite spending several years in and out of psychiatric wards Mostow's disturbing behavior grows and he ultimately becomes a serial-killer who murders males and mutilates into horrific human "gargoyles" via viciously deforming their faces.

After being caught by FBI Mostow is secured in a psychiatric prison, yet he still claims that his actions were those of the demon and continues to obsess over the drawings he keeps with himself in the cell - this leads to strange events as more murders and mutilations occur even after he is imprisoned, which is ultimately revealed to be the work of Bill Patterson, who also claims to be possessed by the same Gargoyle.