Gandalf the Gray is a character in JRR Tolkien's The Lord of the Rings. That name is the best-known guise of the /Maia of the people of Manwë and /Varda whose true name is Olórin. He is said to be one of the wisest of that order.
He came to Middle-earth in the /Third Age as a wizard who counsels and assists other characters and instigates various adventures, sometimes against their wills. In Elvish, he is known as "Mithrandir."