I did not like this take on King Arthur, whom appears during the Dark Swan saga. He is the King of Camelot and he knows of Merlin.

He appears to be a friend to the people of Storybrooke.

But he had his own selfish goals so he was more evil than good.

Hades sends him to the Underworld after the Dark Swan/Merlin story.

And he never returns to the land of the living. But I think he found a good role in the Underworld if I recall right.