megalomania n. folie de grandeur [French]

In the end, she said, [Paul] Rusesabagina had been brought down by hubris — his deluded conviction that it was he, not Kagame, who could heal Rwanda. “It was folie de grandeur.  After he became famous, everyone was telling him, ‘Paul, you could be president.’”  (Joshua Hammer, “He Was the Hero of Hotel Rwanda; Now He’s Accused of Terrorism,” The New York Times, 3/2/2021.)

This word, when used in the above sense, can also be a synonym for self-importance, egotism, conceit  and narcissism.