Like all Yugopotamians, the King fears things that are nice, cute, and sweet; and considers things that are disgusting, scary, or violent to be appealing. When he thought his planet was under threat of invasion from Earth, he tried a number of responses: writing an angry letter, pouting, and then finally dropping a bomb made of candy (which is considered lethal to Yugopotamians) on the planet. Since it was Halloween, all the kids simply gathered the candy and ate it.
King Gripullon and his wife, Queen Jipjorrulac, rule the planet of Yugopotamia with an iron fist: Their subjects don't seem to care, and like being ruled by monarchs. The King arranged a marriage for his son, Mark, with the Boudaician princess, Princess Mandie, who is beautiful by human standards but hideous by Yugopotamian standards. The King and his son also had a tendency to take advantage of the Queen, who responded by taking over the planet when she got a hold of Poof and was able to use his cuteness to subjugate all the Yugopotamians.