Firefoot
From Tolkien Gateway
Firefoot was the horse ridden by Éomer of the Rohirrim, at least on the journey from Edoras to Helm's Deep (during which Gimli was also a passenger on Firefoot's back). Firefoot is never specifically described, but we can probably gain an impression of the animal's appearance from the other horses of Éomer's éored: large and grey-coated with a braided mane and a long tail.