The foolish belief that one is god

One word substitute is Theomania.

Blasphemy: the action or offence of speaking sacrilegiously about God or sacred things; profane talk.
Theocracy: a system of government in which priests rule in the name of God or a god.
Paranoia: a mental condition characterized by delusions of persecution, unwarranted jealousy, or exaggerated self-importance, typically worked into an organized system. It may be an aspect of chronic personality disorder, of drug abuse, or of a serious condition such as schizophrenia in which the person loses touch with reality.
Theomania: a mental illness in which the patient believes him/herself to be a god or to be possessed by one.