Gandalf and Sauron

[Mithadan]

Tolkien conceived of the Valar and Maiar as spirits capable of "clothing" themselves in physical bodies, yet being capable of shedding or changing their "clothing" or appearance at will. However, they could also become incarnate in a permanent physical body, becoming bound by it and its weaknesses. The wizards were incarnated in part as a condition of undertaking their tasks. Such physical bodies can be slain. Morgoth and later Sauron both came to inhabit such physical bodies, Morgoth apparently as a function of his having expended so much of his power, and Sauron as a function of his loss of the Ring.