megalomania; delusions of grandeur
A psychiatric term for a condition characterized by grandiose delusions about one's own importance, power, or abilities. Also used more loosely to describe an exaggerated sense of self-importance.
See also: 誇大妄想 (こだいもうそう)
His megalomania developed into a delusion that he was the chosen one to save the world.
The dictator's megalomania caused enormous suffering to the people.