The Wendigo is commonly described as being emaciated, with its skin pulled tautly over its bone. It's skin is said to be dessicated, its complexion that of death. The eyes are appear to have been pushed deep into the creature's sockets. One person described the Wendigo to look "like a gaunt skeleton recently disinterred from the grave." It's lips, or rather, what remains of them, are said to be tattered and bloody. Some common depictions of the Wendigo give the creature the head of an elk or similar creature.
There are two ways for one to become a Wendigo, each belonging to numerous tribes from the Algonquian region. The first is simply cannibalism. The eating of another human would turn a person into a Wendigo no matter what, similar to the effects of a full moon on werewolves. The other is by possession. A person is possessed by a Wendigo and will immediately start searching for food, no matter how much they have left. Once they are forced to resort to cannibalism, they will turn into a wendigo.