People since time immemorial have been fascinated by the problem of evil; some consider it a philosophical (why does evil exist?) and religious problem (Why does god allow evil if he is omnipotent and benevolent?) while some others have taken a more scientific approach.
Prominent psychologists from Roy Baumeister to Simon Baron-Cohen have written about evil and I first got drawn into psychology when I read ‘The anatomy of human destructiveness‘ by Erich Fromm in 1992, while still in college. As a matter of fact Fromm first came up with the term ‘malignant narcissism’ which was a sort of predecessor to the modern theory of an evil personality.
The modern theory of evil personality has recognized the existence of a dark triad- Narcissism, Machiavellianissm and Psychopathy, and recent studies and conceptualization have extended this to include a fourth trait called Sadism to make it a dark tetrad.
Research has shown that these four traits are moderately correlated to each other but are separate constructs.
But first lets understand what we mean by these terms.
Sadism: Everyday sadism, includes but is not limited to sadism in a sexual context. Put simply, it is a tendency to take pleasure in inflicting pain on others, either directly or vicariously. Normally, if we hurt someone else we feel guilt and shame and distress etc; sadists instead become addicted to such hurting others events as they feel diminished negative affect in hurting someone and instead feel pleasure.
Narcissism: Narcissists have a grandiose sense of self; they also feel very entitled; they are exploitative and demonstrate attention-seeking behavior.
Machiavellianism: Machiavellianism is basically having no qualms in manipulating people; they are also very good at such manipulations and are calculating and cold in their calculations..
Psychopathy: Psychopaths, apart from demonstrating anti-social behavior, are characteristic by their callous and unemotional attitude towards others people suffering. some people believe they lack empathy, while others believe they can cognitively know what it feels like, but do not affectively feel in the same way as their victims.
There is a rich body of literature linking the dark tetrad to many negative outcomes ranging from over-representation in internet trolling to more juvenile delinquency.
There is also some evidence linking these traits diffferentially to the big HEXACO/big five traits. for eg. Narcissism is associated with Extraversion, while Machiavellianism is associated with less Agreeablness; Sadism with less Emotionality, while Psychopathy with less Conscientiousness. The lowered scores on Humility-Honesty dimension of HEXACO are associated with all the four dark triad traits.
Similarly, the traits react differently when provoked: Narcissists aggression is insecurity driven; sadistic persons pleasure driven while that of a psychopath revenge driven.
Referring to my previous post, one can even conjecture that sadism is the Life schema/ Pain-pleasure axis gone wrong; Narcissism is due to inflated self schema; Machiavellianism a result of dysfunctional Others schema, while Psychopathy tied to deficiencies in the World schema.
It would be a mistake to presume that this dark triad is a categorical difference- its a dimensional difference and of degree rather than kind. All of us demonstrate some Machiavellian behavior or say everyday Sadism and its only a matter of time if these tendencies go unchecked you end up on the other side. As the popular saying goes, there are two wolves inside of us, the one which grows depends on which wolf you feed.