Gandalf is the wizard who advises Bilbo and Frodo in J.R.R. Tolkien’s Middle-earth stories.
Gandalf helps initiate Bilbo’s adventure in The Hobbit and later investigates the true nature of Bilbo’s ring. In The Lord of the Rings, he confirms that the ring is the One Ring and urges Frodo to leave the Shire. He then works with the Free Peoples against Sauron.
Gandalf is one of the Istari, supernatural beings sent to Middle-earth to oppose Sauron. His original form is Gandalf the Grey. After confronting the Balrog in Moria, he returns as Gandalf the White, taking a stronger leadership role.
Saruman is also an Istar, but he becomes corrupted by the desire for power. Radagast is another Istar associated with animals and nature. Alatar and Pallando are the two less-documented Blue Wizards, so none of those names identifies Bilbo and Frodo’s principal guide.