Thetis But to conquer the nereid Thetis was not an easy task for Peleus, since she, as Proteus 2, could change her form, becoming in the arms of anyone who strived to hold her, a bird or a tree. So far Peleus clung on her, but when she showed herself in the guise of a tigress, he lost his courage, and loosed his hold. Quoted from website: Parada, Proteus 2