Megalomania

Megalomania (from the Greek word μεγαλομανία) is a psychopathological condition characterized by delusional fantasies of wealth, power, or omnipotence - often generally termed as delusions of grandeur. It includes an obsession with grandiose or extravagant things or actions. It is sometimes symptomatic of manic or paranoid disorders.

In fiction
Megalomania is portrayed very often in fiction, usually as an affliction of supervillains. It is not always used in a strictly correct manner; for instance, it is common for a villain to be described as a "megalomaniac" if he demonstrates an obsession with gaining immense power and wealth (rather than a delusion that he already possesses these things). However, fiction also contains genuinely megalomaniacal supervillains, and the lesser sense of an obsession with grandiose or extravagant things or actions is a common supervillain trait.

Charlie Chaplin parodied megalomania in The Great Dictator, his classic movie comedy about Adolf Hitler.