Chehre pe chehra (1981)

Dr. Wilson is a humanitarian, and likes to believe that the worse part of a human can be separated and eliminated altogether, to this extent he experiments in various ways in his laboratory. One day he tries out a chemical solution on himself and lets his evil self, Blackstone, lose in bars, dark alleys, and with prostitutes. He is always able to control Blackstone, and comes home late at night to turn himself back to Dr. Wilson. Then things start to get out of control when Blackstone starts getting violent and killing people he dislikes, including Dr. Wilson; and Dr. Wilson finds Blackstone getting stronger, and out of his control, with a motive of taking over Dr. Wilson's life completely.