Narcissistic personality disorder (NPD) is a personality disorder defined by the Diagnostic and Statistical Manual of Mental Disorders, the diagnostic classification system used in the United States, as "a pervasive pattern of grandiosity, need for admiration, and a lack of empathy." [1]
The narcissist is described as turning inward for gratification rather than depending on others, and as being excessively preoccupied with issues of personal adequacy, power, and prestige.[2] Narcissistic personality disorder is closely linked to self-centeredness. It is also colloquially referred to as "the god complex".

DSM IV-TR criteria
A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration, and lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by five (or more) of the following:[1]
has a grandiose sense of self-importance
is preoccupied with fantasies of unlimited success, power, brilliance, beauty, or ideal love
believes that he or she is "special" and can only be understood by, or should associate with, people (or institutions) who are also "special" or of high status.
requires excessive admiration
has a sense of entitlement
is interpersonally exploitative
lacks empathy
is often envious of others or believes others are envious of him or her
shows arrogant, haughty behaviors or attitudes