Enemy of Sauron

A title of Gandalf, claimed by himself at the end of the Third Age after his efforts had brought about the downfall of the Dark Lord. It encapsulated his purpose in Middle-earth, and with the destruction of Sauron and his realm, Gandalf left the Mortal lands and returned into the West.

The title is in fact used elsewhere, in a description of Gandalf in the essay The Istari in Unfinished Tales. There it's used of him specifically, even above the other Wizards, to contrast him directly with Sauron. Gandalf's spirit is there called the 'fire that kindles' in direct opposition to Sauron, the 'fire that devours and wastes'. It's clear from this that Gandalf had a particular role as Sauron's direct opposite, even among those of his own order.