Shadowfax originally was owned by Theoden King of Rohan. Shadowfax was a wild stallion too hard to tame. So Theoden decided to give Shadowfax to the wizzard Gandalf the White.

Shadowfax is described as silvery white in daylight, and barely visible at night.

Shadowfax was a superior breed of horses by the name of Mearas that were owned by the kings of Rohan. Shadowfax was the most precious horse and the only person able to ride him was the "Lord of the Rings" who was Gandalf. Shadowfax was "Lord of Horses"

The "Lord of the Rings" is a book written by J.R.R.Tolkien in 1948. and later made into a movie in2001

Gandalf spent time following Shadowfax to tame him for twenty miles and many days Shadowfax had the ability to understand human language and so they bonded over time.

In the making of the movie "Lord of the Rings" Blanco, an Andalusian was one of two horses that played Shadowfax.

The other was Domero another Andalusian Stallion. Blanco bred in New Zealand who died in 2014 at age 25.

More Info: lotr.fandom.com