A person who suffers from a mental disorder characterized by delusions of grandeur, wealth, and power. Plenty of politicians and political pundits are undiagnosed megalomaniacs, as are most Everything noders.
But not me! That fact alone should be proof enough that I deserve to be put in charge of Everything! No one else has the brains, charisma, or force of will! Oh, they laughed at me once, but I'll show them! I'll show them all!