The Brothers Grimm 
Iron Hans 

In Iron Hans a series of huntsmen disappear in a mysterious forest. It is eventually discovered that an iron-skinned man is dragging passersby into the lake where he lives. The man is captured by the king and subsequently released by a sympathetic prince, who then must flee the kingdom. The prince, with the help of the iron-skinned man defeats an army and wins the hand of a princess. The prince is reunited with his parents and Iron Hans is revealed to be a normal man who was under a spell and released from it by the prince who was found to be pure of heart.