Mark Lewis is a  serial-killer and the protagonist of the 1960 British horror film Peeping Tom.

Mark Lewis is depicted as being an unstable man who was subjected to intense abuse by his psychologist father as a child - which may well have contributed to his ultimate descent into madness. His father often exposed him to sadistic experiments, in order to study fear and the body's reaction to it. His father then filmed Mark in his most frightened state of mind.

As an adult Mark Lewis saw himself as a documentary maker but was in reality a merciless killer who would murder women and record their agonizing final moments so as to capture their dying expressions of terror, achieving this using a portable movie camera. In order to make his victims exhibit the most possible fear they can, he places a mirror above his camera and forces his victims to watch their own deaths. His camera has a sharp blade on the end of one of the legs, which he uses to murder his victims.

It appears as if Mark suffers from some sort of mental illness. He often tells those he cares about not to become afraid around him, indicating that if he sees fear in the eyes of people, he becomes compelled to film and murder them. At the end of the film, Mark's love interest, a woman named Helen, discovers the film and is horrified. Mark explains everything to her, and before the police arrive, Mark films himself committing suicide with his camera.