Emotionally shallow, impulsive, and easily bored. Often charming and manipulative. Lacking in empathy and conscience. Potentially brutal. Sometimes as crazy as shit-house rats. Psychopaths, particularly those who are spectacularly violent, offer endless fodder for writers and film-makers.
These characters vary dramatically, spanning a wide continuum. Some have explosive rages; others are unflappably calm. Some are on the wrong side of the law, and others manage to play within the rules. But they all share lack of empathy and connection to others along with a penchant for some form of cruelty.