Characters like Tommy Udo in the 1947 film "The Kiss of Death" and Cody Jarrett in "White Heat" (1949) played to people's misunderstanding that "genre villains," such as gangsters or mad scientists, typified psychopathy.
"They were often caricatured as sadistic, unpredictable, sexually depraved, and emotionally unstable with a compulsion to engage in random violence, murders, and destruction," the team wrote, "usually presenting with a series of bizarre mannerisms, such as giggling, laughing, or facial tics, often creating famous and unreal characters."