The Forest of Hours — Kerstin Ekman

This novel begins in the Middle Ages when Skord, a magical being who is neither man nor animal, finds himself in a forest with no memory, no past and no language. As he observes the behaviour of the human beings he meets in the forest, he begins to gradually understand human civilization and learn their language. Although he can pose as one of them, he is also able to assume the form of animals and cause things to happen simply by willing them. Skord survives for five hundred years and lives many different lives but, despite his learning, he finds it difficult to resist the call of the forest and returns there periodically to rejoin the band of forest outlaws who live outside human society.