Megalomania
Defined in 1 dictionary — Black's (1910)
Black's Law Dictionary
Henry Campbell Black, M.A. · 1910
The so-called "delirium of grandeur" or "fulie de grandeur;" a form of mania in which the besetting delusion of the patient is that he is some person of great celebrity or exalted rank, historical or contemporary.
Defined under Insanity in Black's Law Dictionary.