Arod is the horse of Rohan who Legolas rides into the Paths of the Dead. (He first appears in The Two Towers; look for him in our "Character Analyses" in that learning guide if you're dying to know more about him.) Arod does not want to go through the Dark Door to this evil place, but Legolas puts his hands over Arod's eyes and sings to him so that Arod can keep chugging along. Arod also bears Legolas and Gimli away from Minas Tirith in the final chapters of the novel. For all of his (understandable) fear of dead people, he has been a trusty horse for Legolas and Gimli.
Gwaihir is the greatest of the great eagles who fly into battle with Aragorn's troops against Mordor. Gwaihir has also been turning up periodically throughout the series: He is the eagle who rescues Gandalf from the top of Saruman's stronghold Orthanc in The Fellowship of the Ring. He is also the one who carries Gandalf from the peak of Zirakzigil, one of the Mountains of Moria, to Lothlórien in The Two Towers. So Gwaihir is a convenient ally for Gandalf to have. (For reasons why we think he's a little too convenient, check out our "Character Analyses" of Gwaihir in The Two Towers learning guide.)
Gandalf asks Gwaihir for one last favor in front of the Morannon (also known as the Black Gate of Mordor). He wants Gwaihir to carry him to the peak of Mount Doom. Gwaihir also brings his brother, Landroval, and Meneldor, who is young and fast. They go in search of Frodo and Sam on the exploding peaks of Mount Doom. This is a seriously handy eagle to have on your team.
Landroval is Gwaihir's brother, also a descendent of Thorondor, "who built his eyries in the inaccessible peaks of the Encircling Mountains when Middle-earth was young" (6.4.3). Landroval accompanies Gwaihir to Mount Doom to pick up Sam and Frodo after the last battle.
Meneldor is one of Gwaihir's eagles. He flies with Gwaihir and Landroval to Mount Doom to find Frodo and Sam after the destruction of the Ring.
This is Aragorn's horse, which the Rangers have brought with them from the North. (Up until now, Aragorn has been riding Hasufel, a horse of Rohan whom Éomer loaned to Aragorn in The Two Towers Book 3, Chapter 2.)
Scatha the Worm is a dragon whose hoard is the source of the ancient horn that Éowyn and Éomer give to Merry. Apparently, Eorl the Young brought this horn with him from the North before settling in Rohan.
Shadowfax is Gandalf's super-awesome, super-gorgeous superhorse—the best and fastest horse born to the horse-lords of Rohan in the day of Théoden King. Even after days of riding, Beregond observes that, "He looks as if he were spoiling for a race" (5.1.118). Gandalf rides Shadowfax without a saddle, because if Shadowfax wants to carry someone, he will. Otherwise, no bridle will tame him. Shadowfax is also the only horse in all of Middle-earth who can stand calmly in front of the Lord of the Nazgûl, as Shadowfax does when Gandalf confronts the Witch-king of Angmar at the gates of Minas Tirith. For more on this speedy animal, check out our "Character Analysis" in The Two Towers.
Shelob is the horrifying spider creature that bites Frodo at the end of The Two Towers, poisoning him and leading Sam to believe that Frodo has died. For a blow-by-blow account of the showdown between Frodo, Shelob, and Sam, see our The Two Towers learning guide "Chapter Summary" of Book 4, Chapter 9.
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Snowmane is Théoden's horse. In the Battle of the Pelennor Fields, the Lord of the Nazgûl hits Snowmane with a black dart. When Snowmane falls, so does Théoden. In Snowmane's agony, the horse also crushes its master. So Théoden dies as a result of Snowmane's fall. The Riders of Rohan dig a grave for her and leave a tombstone: "Faithful servant yet master's bane,/ Lightfoot's foal, swift Snowmane" (5.6.40). It proves how much the horse-lords really do love their horses that they extend this honor to their king's horse, even though Snowmane accidentally killed the poor man.
Strider is Sam's second pony, a companion to Bill. We don't know how Aragorn feels about his name being used for Sam's pony, but we're hoping he gets a laugh out of it.
Stybba is Merry's hill pony, which he receives so that he can ride alongside Théoden to Dunharrow. But Stybba isn't fast enough to take Merry to Gondor with the Riders of Rohan. So Merry has to take up with "Dernhelm."
Quickbeam is another Ent whom Merry and Pippin befriended in The Two Towers. He is the one who hands over the keys to Orthanc to Aragorn.
Windfola is the name of Dernhelm/Éowyn's horse. He carries Merry and Éowyn right to the Battle of the Pelennor Fields, but once the Nazgûl arrive, Windfola throws them and runs off in terror. He now "[runs] wild upon the plain" (5.6.8).