Of Unknown Origin is a 1983 psychological horror film directed by George P. Cosmatos in his North American film debut, and starring Peter Weller, Jennifer Dale, Lawrence Dane, Maury Chaykin, Kenneth Welsh, Louis Del Grande and Shannon Tweed in her film debut. Based on the 1979 novel The Visitor by Chauncey G. Parker III, it focuses on 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 that rats have no known origin.