Often, the term 'psychopath' tends to be equated with violent and deranged criminality, but true psychopaths are very different from the way they are portrayed in film or on television. They are aware of the difference between right and wrong: they simply choose to ignore anything that prevents them getting what they want.

Real-life psychopaths are not 'mad' but 'bad', but they appear on the surface to be entirely 'normal'. One of the pioneers of the modern research effort was Dr. Robert Hare, who developed the Psychopathy Check List Revised (PCL-R) in an attempt to describe the degree of psychopathy an individual displays.

The clusters of personality traits and socially-deviant behaviours outlined in the check-list are separated into four types: interpersonal, affective, lifestyle and anti-social. The 10 Worst Psychopaths looks at history's most notorious and infamous psychopaths, and seeks to show how their life stories illustrate the classic psychopathic personality traits. Though all morally despicable, many of these individuals were charming, popular and charismatic.

This is part of our enduring fascination with the psychopath: they are capable of extraordinary inhuman acts, and yet they appear on the surface to be entirely 'normal'. It is only once you know what to look for that the psychopathy beneath the cunning mask becomes obvious. Chillingly, psychopaths are usually the person you would least suspect.