King of Eagles
King of Eagles was a title given to Thorondor, the gigantic and noble eagle of the First Age, whose talons wounded the face of Morgoth himself. Thorondor dwelt among the peaks of the Crissaegrim, guarding Turgon's Hidden City of Gondolin from the forces of Morgoth until that city's Fall, and he came to the aid of the Elves many times during the First Age.
In The Hobbit, we meet a character who carries the title 'Lord of Eagles', a title that was also borne by Thorondor in the Elder Days. Whether the title of 'King of Eagles' was also passed down through the Ages like this cannot be known - in Tolkien's other writings, it is only ever used of Thorondor himself.