The Lawnmower Man
The film is based on a short story written of the same name by Stephen King.
A somewhat mad scientist named Dr. Lawrence Angelo (Pierce Brosnan) decides to try out an experimental regimen of pills and computer-simulated training on an unsuspecting landscape gardener named Jobe Smith (played by Jeff Fahey), a man with mental disabilities.
The pills and training begin to work, and Jobe begins to increase in general intellect and mental skills.
But soon, Jobe's increased intelligence allows him to gain psychic powers and he discovers that those around him have simply been using him and he sets out to plot revenge.