The Voyage of the Dawn Treader
by C.S. Lewis
Ramandu is a "star at rest" who now lives in the form of an old man on an island at the eastern edge of the world of Narnia. Along with his daughter, he cares for Aslan's Table and greets the dawn every morning with a song. He is in the process of aging in reverse, and when he becomes young enough he will go back to being a star again.