megalomaniac - n. 1) a person afflicted with megalomania
megalomania - n. 1) a psychopathological condition characterized by delusional fantasies of wealth, power, or omnipotence; 2) an obsession with grandiose or extravagant things or actions.
Taken from wikipedia.org:
Diagnostic criteria
At least five of the following are necessary for a diagnosis:
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 unique and can only be understood by other special people
requires excessive admiration
strong sense of entitlement
takes advantage of others to achieve his or her own ends
lacks empathy
is often envious or believes others are envious of him or her
arrogant affect.
http://en.wikipedia.org/wiki/Narcissistic_personality_disorder
See also:
http://en.wikipedia.org/wiki/Superiority_complex
Superiority Complex refers to a subconscious neurotic mechanism of compensation developed by the individual as a result of feelings of inferiority. The term was coined by Alfred Adler (February 7, 1870 – May 28, 1937), as part of his School of Individual Psychology.
Those exhibiting the superiority complex commonly project their feelings onto others they perceive as inferior to themselves. Accusations of arrogance and cockiness are often made by others when referring to the individual exhibiting the superiority complex.
Behaviors related to this mechanism may include an exaggeratedly positive opinion of one’s worth and abilities, unrealistically high expectations in goals and achievements for oneself and others, vanity, extravagant style in dressing (with intention of drawing attention), pride, sentimentalism and affected exaltation, snobbism, a tendency to discredit other’s opinions, forcefulness aimed at dominating those considered as weaker or less important, credulity, and others.
Social aloofness, daydreaming, isolation could also be associated to the Superiority Complex, as a way to evade the fear of failure related to the feelings of inadequacy to face real world.
Superiority and Inferiority Complex are often found together as the different expressions of the same pathology.