A person who could take on the appearance and nature of an animal at will or under the influence of extreme emotion. In The Hobbit Beorn  is a skin-changer, taking the form of a bear, although Tolkien does not mention in what way this takes place. He gives no clue as to whether Beorn's skin actually changes, whether he wears the skin of a bear or whether he has shamanic powers and can send forth a 'fetch' of himself in bear form as an out-of-body experience.