In The Lord of the Rings: The Two Towers, Gandalf is the wizard who returns in white. He reappears after falling with the Balrog in Moria during The Fellowship of the Ring.
At the start of The Two Towers, Aragorn, Legolas, and Gimli encounter Gandalf in Fangorn Forest. He explains that he fought the Balrog and returned to Middle-earth as Gandalf the White. His new form reflects an increase in authority and power.
Gandalf the White takes the place of Saruman as the chief opposing force among the wizards. He later helps free King Théoden from Gríma Wormtongue’s influence and arrives at Helm’s Deep with reinforcements at dawn.
Gandalf’s return is sometimes confused with a simple change of clothing. In the story, it represents a transformation after his battle with the Balrog and his renewed mission against Sauron.