Gwaihir is the lord of the Great Eagles and a friend of Gandalf.
Background
Gwaihir was descended from Thorondor, the greatest Eagle who ever lived. It was said that he and his brother Landroval aided Thorondor in rescuing Beren and Luthien from Angband.
At some point in his life, Gandalf the Grey saved him from a poisoned arrow and the two became friends.
Appearances
The Lord of the Rings
The Great Eagles flew far and wide and gathered news of the Nazgûl and the mustering of Orcs and Wargs, and of the escape of Gollum from Mirkwood. Gwaihir saved Gandalf from Saruman's captivity on Orthanc and delivered him to Rohan. He later rescued Gandalf after his battle with there Balrog.