Megalomaniac

Megalomania is defined as:
[1] A psychopathological condition characterized by delusional fantasies of wealth, power, or omnipotence.
[2] An obsession with grandiose or extravagant things or actions.

"The megalomaniac differs from the narcissist by the fact that he wishes to be powerful rather than charming, and seeks to be feared rather than loved. To this type belong many lunatics and most of the great men of history." - Bertrand Russell

Delusions of grandeur are principally a subtype of delusional disorder but could possibly feature as a symptom of schizophrenia and manic episodes of bipolar disorder. Grandiose delusions are characterized by fantastical beliefs that one is famous, omnipotent, or otherwise very powerful. The delusions are generally fantastic, often with a supernatural, science-fictional, or religious bent. Grandiose delusions are distinct from grandiosity, in that the sufferer does not have insight into his loss of touch with reality.

"Megalomaniac", Incubus