Haneul is part Haetae – an extinct people who were shape-shifting lions – and part Fey, and currently rules the magical domain of North and South Korea. He’s possibly allowed to do this because he doesn’t interfere often, except to maintain his position.
When anyone tries to wrest the title from him, he eats them. Other than that, he doesn’t get involved much. No one doubts his power, but influence is another question entirely.