King Utopus has the distinct honor of being the only actual Utopian character in the whole book. Odd, it seems, for a book supposedly all about Utopia. Or maybe not.
Consider that Hythloday identifies pride—you know, the "all me, all the time" sin—as the most damaging fault in Europe and also as the sin least present in Utopian society. In Utopia, he paints a picture of a world in which individual accomplishment and notoriety don't really have a place, so why would we get to meet lots of individual characters? That would undermine his whole project.
King Utopus gets a special shout-out because he is Mr. Nation-Founder. Kind of like King Arthur is to Britain, King Utopus is to Utopia: a semi-mythological figure that helps a country define its identity. Maybe this account of Utopus will sound familiar:
"But Utopus, who conquered the country and gave it his name (for it had previously been called Abraxa), and who brought its rude, uncouth inhabitants to such a high level of culture and humanity that they now excel in that regard almost every other people, also changed its geography" (2.43).
By making Utopian history/mythology sound similar to European history, More can also suggest that these two radically different places didn't start off so differently. So maybe Europe could become like Utopia? Maybe they're not so alien after all...