King Thrushbeard has always been one of my favorite fairy tales. Top five, easily. (The top five, in no particular order: King Thrushbeard, Prince Lindworm, Donkey Cabbages, East of the Sun West of the Moon, and Beauty and the Beast.) This is partly because (spoiler) I'm a total sucker for secret identities (I blame this on early exposure to Robin Hood and The Princess Bride), and I think partly because of a blog post I read years and years and years ago, which analyzed King Thrushbeard as a Christian allegory. It was a really fascinating post, and I wish I could link it for you, but I first encountered it over a decade ago, and I wouldn't know where to even begin looking for it now.