How about a dragon how cheerfully rules over a kingdom; his people all know him for what he is, and dragons are looked upon as wise and benevolent creatures. Dragonslayers from other kingdoms coming to free it from 'tyranny' are likely to get beaten to death by peasants with cast iron skillets.
Someone needs the blood of a dragon, given willingly, to make a rare potion. Guess who gets hired to sweet-talk a dragon into giving up some highly powerful blood?
One morning, the sun does not rise. It seems that a great darkness has settled across the kingdom - at first, it is merely an inconvenience, but as time passes and plants begin to sicken and die, some action must be taken. As the deluded King plans the sacrifice of fifty tender virgins in the name of the Sun God, rumours spread of an ancient barrow uncovered in the hills...