The Great Eagles are said in The Silmarillion to have been "devised" by Manwë Súlimo, leader of the Valar, and were often called the Eagles of Manwë. They were sent from Valinor to Middle-earth to keep an eye on the exiled Ñoldor, and also on their foe the evil Vala Morgoth.
The Great Eagles were the messengers and spies of the King of Arda, and possessed the ability to see through all physical matter except for the blackness of Morgoth's evil pits. They were possibly Maiar who derived their abilities and shape from Manwë himself, but that is mere speculation. Morgoth first discovered the limits of their sight prior to the fall of the great stronghold of Utumno. The king of these eagles was Thorondor and descendents of his included the eagle lord Gwaihir, who carried Gandalf many times during the Third Age.
For a time the Lord of the Eagles, Thorondor, kept his eyries at the top of Thangorodrim, the three mighty peaks that Morgoth raised from the Iron Mountains above the gates of Angband. While they lived there, Thorondor helped Fingon rescue Maedhros. Thorondor's folk later removed their eyries to the Crissaegrim, part of the Echoriath or Encircling Mountain about Gondolin. There they were friends of Turgon, and kept spies off the mountains.
Thorondor wounded Morgoth in the face after Morgoth's battle with Fingolfin, and carried Fingolfin's corpse to the Echoriath, where Fingon buried him.
In the Second Age, a pair of Eagles had an eyrie in the King's House in Armenelos the capital of Númenor until the Kings became hostile to the Valar. The Eagles also watched the peak of Mount Meneltarma, and three Eagles would always appear when someone climbed to the summit.
Towards the end of Númenor, the Valar sent storm clouds in the shape of Great Eagles in an attempt to warn them of their folly and impending doom.
Third AgeThe Hobbit, no eagles were identified by name. Only the title Lord of the Eagles distinguished the eagle leader from other eagles in this story. (The text added that he was given the title King of All Birds at a later date.) Many readers assume that it was Gwaihir and Landroval who rescued Thorin Oakenshield and company from a band of Wargs and Goblins, flying them to the river Anduin, and later assisting in the Battle of the Five Armies fought near Lonely Mountain (Erebor). However, in Return of the King Gandalf says that Gwaihir has carried him twice before, while the proper count would be three times if Gwaihir and the Lord of the Eagles were the same individual.
Before and during the War of the Ring, Gwaihir rescued Gandalf the Grey from the top of Isengard and again from Zirak-Zigil. The Eagles aided troops of King Elessar at the Battle of the Morannon at the Black Gate. The Eagles arrived in time to overthrow some Názgul, including Khamûl. Gwaihir, with others of his people, rescued Frodo Baggins and Samwise Gamgee from Mount Doom in Mordor after the One Ring had been destroyed.
Behind the Scenes
Tolkien's painting of an eagle on a crag appears in some editions of The Hobbit. According to Christopher Tolkien, the author based this picture on a painting by Archibald Thorburn of an immature Golden Eagle, which Christopher found for him in The Birds of the British Isles by T. A. Coward. However, Tolkien's use of this model does not necessarily mean that his birds were ordinary Golden Eagles. In some of his texts Tolkien speculated that these great Eagles were actually Maiar in bird-shape, as he felt it unlikely Ilúvatar would grant feär to animals. If this is true, then Roäc the Raven and the Thrush, who appear in The Hobbit, might also be Maiar or other spirits in animal form (and possibly even Beorn, who sometimes takes the form of a bear).
Named Great Eagles
Races of the Creatures of Arda