Gandalf is the wizard who leads the Balrog away during the Fellowship’s escape from Moria in J.R.R. Tolkien’s The Lord of the Rings.
On the Bridge of Khazad-dûm, Gandalf confronts the Balrog after the creature pursues the Fellowship. He breaks the bridge beneath it, but the Balrog’s whip catches him and pulls him into the abyss. Gandalf and the Balrog then continue their struggle through the depths of Moria and up to the mountaintop of Zirakzigil.
After defeating the Balrog, Gandalf dies from his wounds, but he is sent back as Gandalf the White. His return marks a major transformation: he replaces Saruman as the chief opposing wizard in the struggle against Sauron and carries greater authority.
The Balrog is not an ordinary monster; Tolkien identifies it as a fallen spirit of the same broad order as Gandalf, though aligned with evil. Saruman and Radagast are also Wizards, but neither fights this Balrog.