Gandalf is the wizard known as Olórin in J.R.R. Tolkien’s mythology.
Olórin is Gandalf’s name in Valinor, where he belongs to the Maiar, spiritual beings who serve the Valar. He is sent to Middle-earth as one of the Istari, the five wizards dispatched to oppose Sauron and encourage resistance among the peoples of the world.
In The Hobbit and the early part of The Lord of the Rings, Gandalf appears as Gandalf the Grey. After fighting the Balrog beneath Khazad-dûm, he returns as Gandalf the White, taking Saruman’s intended place as the chief opposing force against Sauron.
Gandalf has other names across Tolkien’s languages and cultures, including Mithrandir among the Elves and Men of the West. He is not the same kind of being as Sauron, although both are Maiar; their purposes and loyalties are fundamentally opposed.