J.R.R. Tolkien’s wizard who guides Frodo is Gandalf.
Gandalf is one of the Maiar, spiritual beings sent to Middle-earth to oppose Sauron. He arrives there in the form of an old man and is known first as Gandalf the Grey. His wisdom, travels, and understanding of the Ring make him a crucial protector of Frodo and the Fellowship.
Gandalf investigates Bilbo’s ring and recognizes that it is the One Ring. He then helps organize the journey from the Shire and joins the Fellowship. After confronting the Balrog in Moria, he returns as Gandalf the White, with greater authority and a changed role.
Saruman is another wizard and was originally the head of the order, while Radagast is a separate wizard associated with animals and the wild. Neither is Frodo’s principal guide.