Hmmm... it's hard to get some of those miniatures that Jon pointed out... out of my head. I personally like this notion of him (to the right), so maybe that's influencing my opinion.
I think I see him as taking himself very seriously, though others might snicker behind his back... until he nails one of them. Definitely not too diminuative, so maybe the height of the Dwarf or Pixie. And especially if his final version includes no way to whack him. Unless you want to go for something more literal, like this... http://a0.vox.com/6a...d6b07fe80005-pi
Also, have you thought of a motif for his persona card? The Reaper has his own unique card in that, so I suppose the King might too. I've had notions of trying to create a persona/NPC style card, since there are others working some different angles on such creations. Something like has been done for characters, the alt endings, etc., with a common format to identify what they are. But maybe the King needs something unique just for him.