Gandalf is the wizard known as Mithrandir in J.R.R. Tolkien's Middle-earth.
Mithrandir is a Sindarin name meaning “Grey Pilgrim,” reflecting Gandalf's wandering life and his appearance as Gandalf the Grey. The name is used especially by the Elves and by people familiar with the languages of Middle-earth.
Gandalf is one of the Istari, supernatural beings sent to Middle-earth to oppose Sauron. He arrives in the form of an old man and works through advice, courage, and leadership rather than ruling kingdoms directly.
After confronting the Balrog in Moria, Gandalf returns as Gandalf the White. Saruman and Radagast are also Istari, but Mithrandir is Gandalf's name, not theirs. Tolkien used several other names for the character, including Olórin and Tharkûn.