Demon King Demaon (大魔王デマオン) is the ruler of the demon realm and the main antagonist of Nobita's Great Adventure into the Underworld and its remake, Doraemon: Nobita's New Great Adventure into the Underworld – The Seven Magic Users.
For many thousand years, Demaon has desired to conquer Earth which is his ideal planet for his demon race. It was widely believed that he was influenced by great disasters on Earth such as Cretaceous Paleogene extinction event, the great flood, and the more recently, various natural disasters in modern day. Apparently, Demaon had no interest in recruit any life form on Earth for his cause until met humanity, where he and his kind taught them ancient sorcery which is darker than modern day sorcery.
However, mankind soon learned the darkness within Demaon and banished him and his kind back to his homeworld, but not before Demaon left his dark knowledge in some ancient grimoires that scattered across the world. Nirnaeth was one of the rebelling humans who documented demons and dark magic's susceptibility with the moonlight, having created a seal on the moon's surface so its power can protect humanity.
Modern Day Invasion
Now Demaon intended to start another invasion again. The time for the invasion finally comes when a desperate woman, Mrs. Mangetsu, contacted him to have her life in exchange for her daughter's recovery. After took her away from Earth and turned her into a demon called Medusa, Demaon granted her wish, before making preparations for the invasion for the next few years.
- His name does not appear in the original movie, and only appears once in the manga.