Throughout his comic book appearances, the Joker is portrayed as a master criminal whose characterization has varied. The original and currently dominant image is of a highly intelligent psychopath with a warped, sadistic sense of humor.
Fictional portrayals of psychopaths, also known as sociopaths, are some of the most notorious in film and literature but may only vaguely or partly relate to the concept of psychopathy, which is itself used with varying definitions by mental health professionals, criminologists and others. The character may be identified as a diagnosed psychopath or sociopath within the fictional work itself, or by its creator when discussing their intentions with the work, which might be distinguished from opinions of audiences or critics based only on a character appearing to show traits or behaviors associated with an undefined popular stereotype of psychopathy.
Such characters are often portrayed in an exaggerated fashion and typically in the role of a villain or antihero, where the general characteristics of a psychopath are useful to facilitate conflict and danger. Because the definitions and criteria in the history of psychopathy have varied over the years and continue to change even now, many characters in notable films may have been designed to fall under the category of a psychopath at the time of the film's production or release, but not necessarily in subsequent years. There are several stereotypical images of psychopathy in both lay and professional accounts which only partly overlap and can involve contradictory traits: the charming con artist, the deranged serial killer, the successful corporate psychopath, or the chronic low-level offender with Juvenile delinquency. The public concept reflects some combination of fear of the mythical bogeyman, fascination with human evil, and sometimes perhaps envy of people who might appear to go through life unencumbered by the same levels of guilt, anguish or insecurity. Comics