Of Unknown Origin is a 1983 Canadian psychological horror film directed by George P. Cosmatos. Based on the 1979 novel The Visitor by Chauncey Parker, it stars Peter Weller as a mild-mannered Manhattan banker, who becomes increasingly obsessive and destructive in his attempts to kill a rat loose in his renovated brownstone. The film's title refers to the misconception (repeated in the film) that rats have no known origin.