Lycanthropy as it is understood now - people shifting shape at fullmoon - did not exist in Middle-earth. However, there were great wolves inhabited by spirits that were of the same origin as the valar and maiar, only lesser. There were only a few of them, though, and they all lived in the First Age serving Melkor (and Sauron) - if you have read the Silmarillion, you probably remember Carcharoth and Draugluin and Tol-in-Gaurhoth. So, I'm afraid a werewolf would be pretty unorthodox of an RPG character.
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