(Image: Warner Bros.)
Atreyu, the great hero of the movie The Neverending Story (and the first half of the novel) rides a magnificent stallion named Artax. In his long journey to find a solution to the Nothing consuming Fantasia, the pair crosses the Swamp of Sadness. There, Artax dies in a haunting scene that almost breaks Atreyu.
Artax is developed in greater depth in the original novel, which I highly recommend. He's is 1 of 16 extraordinary horses of fantasy rounded up by Tor. Other great horses from the list include Brego, which was Aragorn's ride in The Lord of the Rings, and Swift Wind from She-Ra: Princess of Power.