The Dragon King is actually Illiono. Illiono is a hearrsmon warlord who has convinced a powerful (but rather stupid) grand dragon to be his steed. Illiono has been trying to gather a dragon force that will be able to sack and take Myork. He believes that he can give the loot to the dragons, while taking the city for himself. He sees them simply as a means to an end and is becoming too confident for his dangerous situation.
The Dragon King has been raiding some of the more distant Anglic towns, trying to prove to the dragons the ease of the conquest and the rewards. Most of the dragons realize the foolishness of the idea, knowing that the knights of Myork have trained for centuries in the killing of dragons. While a sufficient number of dragons could probably destroy Myork, they would not have the ability to capture the city intact.