Gandalf’s exceptionally swift horse in J.R.R. Tolkien’s The Lord of the Rings is Shadowfax.
Shadowfax is a great horse of Rohan and belongs to the line of the Mearas, animals renowned for intelligence, strength, and speed. King Théoden eventually allows Gandalf to take him, and the wizard rides him during crucial journeys across Middle-earth.
The horse’s name is usually understood as referring to his silver-grey appearance. Shadowfax can run for long distances at remarkable speed, and Tolkien presents him as more than an ordinary mount: he understands speech, chooses his rider, and displays an almost legendary independence.
Readers sometimes confuse Shadowfax with Brego, the horse associated with Aragorn in the film adaptations, or with Asfaloth, the horse ridden by Glorfindel in the book. Those are separate horses. Shadowfax is specifically linked to Gandalf and Rohan.