Skin-changers

Beings who could take different forms at will. Little is known of their abilities; the only skin-changers specifically identified by Tolkien were Beorn and his descendants. Beorn at times took the form of a huge black-haired Man, and at times the shape of a gigantic black bear. This ability was passed down to at least some his descendants, though they were said to be somewhat lesser of stature than Beorn himself.

Beorn is the only skin-changer that we're told about in any detail, so what may have been true for him may not have been true for all other skin-changers, but we do know something of his abilities. He was under no curse or enchantment (except perhaps one that he had placed on himself), and he was able to change between the shape of a Man and a bear at will. He also had the power to communicate with other animals, not only bears (though he could summon those as he needed them), but other animals of all kinds.¹

The origins of Beorn and his strange abilities are unclear. Some suspected that he might have begun life as a black bear in the Misty Mountains, before being driven out by the giants, while others claimed that he was Man of the stock of the Northmen. Gandalf favoured the latter explanation, and indeed there is good reason to think that this is correct: Beorn was almost certainly a Man who could become a bear, rather than a bear who could become a Man.²

In bear form, Beorn apparently became more bear-like in temperament (so that he had to warn his visitors not to wander outside while he was in this shape, implying that he was less able to control his ferocity). Beorn as a bear was tremendously large and strong, and there are indications that he could become even larger and stronger when enraged.³ At the Battle of Five Armies, he was so powerful that even an army of Goblins could not resist his onslaught, and indeed his arrival in that battle turned the tide of the entire conflict.

Beorn and his descendants are the only skin-changers that we know about in any detail at all, and indeed it is conceivable that they were unique in Middle-earth. When Gandalf first mentioned Beorn to his companions, however, he described him with the words, 'he is a skin-changer' (The Hobbit 7, Queer Lodgings). The fact that Beorn was a (not the) skin-changer strongly suggests that there were others (and indeed, from the way Gandalf used the word, it seems as if he expected his audience to know about such beings - though in point of fact Bilbo, at least, did not).

This raises the strong possibility that there were others with Beorn's power, either to turn into bears at will, or perhaps creatures of other kinds. (Indeed, it is not absolutely established that Beorn himself could transform only into a bear, though it is very heavily implied.)

In fact, we know for sure that there were other shape-changers in history, notably the Maiar. The most emphatic example of this was seen in Sauron's battle with Huan during the First Age, in which that Maia transformed himself in turn into a wolf, a serpent, his own usual form, and then a great vampire. Indeed, from this perspective, Gandalf himself was a shape-changer, since the form of an old man that he used in Middle-earth had not been his natural shape before he crossed the Sea. These abilities, though, were part of the nature of a Maia, and there's absolutely no hint that Beorn or his kin were anything of the sort. In that sense, the shape-changing of the Maiar seems to be quite distinct from the skin-changing of Beorn and his kind.

Perhaps a more direct comparison would be werewolves, which certainly existed within Middle-earth. As with the Maiar, though, there are difficulties with this comparison, because werewolves were cursed beings with enslaved wills, while skin-changers like Beorn were certainly not under a curse. Further, it's not completely clear that Tolkien's werewolves actually were shape-changers (at least, we always encounter them in the form of wolves).

So, while it does appear that there were probably other skin-changers like Beorn elsewhere in Middle-earth, and there were certainly shape-changers of other kinds, we never directly encounter any other being with a power directly comparable with that of Beorn.