Many creatures exist within Middle Earth that seemed able to alter their form to that of an animal, and there are hints throughout The Lord of the Rings and The Silmarillion that this is possible. This ability is never fully explained, and as such, is often overlooked or ignored.
Known Shape ShiftersEdit
The Valar are not constricted to any one form, but often choose to take forms similar to the children of Illuvatar.
|“||Their shape comes of the knowledge of the visible world, rather than of the world itself; and they need it not, save only as we use raiment...Therefore the Valar may walk, if they will, unclad, and then even the Eldar cannot clearly perceive them, though they be present. But when they desire to clothe themselves the Valar take upon them forms some as of male and some as of female.||”|
One shape shifter that we do meet in The Hobbit is Beorn. Beorn is a very mysterious character, who lives alone in a house near the Carrock (as he calls it). He is introduced by Gandalf as "a very great person", and a skin-changer, which seems to be akin to a shape shifter, as he is able to change between a man and a bear. In the novel The Hobbit he seems to spend his days as a "great strong black-haired man," and his nights as a "huge black bear." Little is known about his origins, but Gandalf says of him:
|“||Some say that he is a bear descended from the great and ancient bears of the mountains that lived there before the giants came. Others say that he is a man descended from the first men who lived before Smaug and the other dragons came into this part of the world, and before the goblins came into the hills out of the North. I cannot say, though I fancy the last is the true tale. He is not the sort of person to ask questions of.||”|
–The Hobbit: Queer Lodgings
Beorn lived with many animals such as horses and dogs, as well as keeping bees bigger than hornets. These animals were quite intelligent, and even were able to understand Beorn's speech; the dogs were able to walk on their hind legs and carry things with their front paws. It is unknown whether or not these were skin changers as well, as they were certainly not normal animals.
Although not mentioned in the Lord of the Rings, the Silmarillion recounts Sauron's shape-shifting abilities. Sauron is known as the Lord of Werewolves, and is able to change into the form of a werewolf, as when he does battle with Huan.
|“||Therefore he took upon himself the form of a werewolf, and made himself the mightiest that had yet walked the world.||”|
During this struggle, Sauron was not restricted to only a werewolf form.
|“||Then Sauron shifted shape from wolf to serpent, and from monster to his own accustomed form, but he could not elude the grip of Huan without forsaking his body entirely.||”|
It may be that the Maiar, being less powerful versions of the Valar, also share this ability to change their appearance at will. It is not stated that the Maiar were different beings to the Valar entirely. In fact,
|“||With the Valar came other spirits whose being also began before the World, of the same order of the Valar but of less degree.||”|
This would explain Sauron's ability to change at will. There is also evidence to suggest that other Maiar possess this power.
Of Gandalf, Tolkien says,
|“||For though he loved the Elves, he walked among them unseen, or in form as one of them.||”|
Gandalf (and therefore the Istari in general) were able to change their form at least to that of an Elf or Human. Nevertheless, this ability is never explained, only hinted at, and there may be unknown limitations to this power that would explain why it is not more commonly employed.
It should be noted that Werewolves in Arda are not shape shifters; they are limited to only their wolf form, unlike some non-LOTR legends wherein they become men.