I'd be surprised and disappointed if the sheriff is Robin Hood because I don't think Robin Hood is a fairy tale. If memory serves, it is at least debated that he was based on a real person and his story actually did come down through ballads. That being said, I can't think of which fairly tale character he could be. Perhaps he is the huntsman from Red Riding Hood or maybe the prince from Rapunzel, or even the "beast" from Beauty and the Beast? It will be interesting to see the reveal.