A pathological liar is a person who compulsively lies for personal gain and doesn't feel guilt or remorse when hurting other people. Pathological liars are considered to be sociopaths, meaning they have a personality disorder in which there is an absence of conscience and a sense of right and wrong.
Pathological liars are often manipulative and tell lies that are outlandish yet believable. They often present themselves as being either heroic or victimized. However, they are typically aware that they are lying. Pathological liars tell lies because of their sociopathic personality trait, not due to external circumstances. Because pathological liars don't feel guilt or stress due to their actions, their lies are difficult to discern through a lie detector test.