Gandalf is a wizard - one of the Istari, immortal spirits sent to Middle-earth in mortal form to guide and counsel the free peoples in their struggle against Sauron. Known as Gandalf the Grey (and later Gandalf the White), he is the architect of the quest to destroy the One Ring, the driving force behind the alliances that oppose Sauron, and a figure of immense wisdom and power who deliberately restrains himself to let mortals find their own courage. He accompanies Bilbo on the quest to the Lonely Mountain, later guides Frodo and the Fellowship, and falls in battle with the Balrog in Moria - only to return transformed. Gandalf appears in both The Hobbit and The Lord of the Rings as perhaps the most beloved character in all of Tolkien's work.