The term “psychopath” has come in popular use to be understood as a description of an individual who seems to have a clear and rational understanding of the world around them; they are not deluded or suffering from hallucinations and yet they seem to be able to act with great cruelty or with recklessness towards the safety of others and themselves. The medical and legal professions have been struggling for over 200 hundred years to reach agreement on whether there might be appropriate psychiatric diagnoses that might helpfully describe such individuals. Various terms such as moral insanity, monomania, psychopathy, and antisocial personality disorder have been used. The term “psychopath” is the one that has become most firmly fixed in the public imagination. The violence and harm that people with these kinds of problems might do can raise a great deal of public anxiety. This anxiety has often played out and been amplified in various forms of the media. This article traces some of the ways that various forms of popular media have been of crucial importance to shaping our understanding of “psychopathy” and the related diagnoses of moral insanity, monomania, and antisocial personality disorder. From the medical treatises and press reporting of notorious trails, and the explorations of dangerous forms of consciousness in the 19th century, to the way that the mass media, including films, have presented such problems, they have often had a key influence on the legal and medical formulations.