From a young age, even while soaring in the skies, Rock always dreamed of what was beyond. As an adult, he put dreams aside and studied, never quite sating his rapacious hunger to know all there was to know about the world behind the clouds, devouring every scroll he could find, studying with any mystic, sage or iron-foil hat crackpot who would claim expertise or insight. The nights not spent poring over parchment were instead devoted to observation, annotation, extrapolation of the movement of the stars. And that's when he saw it. Some kind of celestial event? An entity? A crack in the sphere? He couldn't say for sure, but he was certain he'd seen something, and that something spelled doom for all unless he took action.
But an aarakocra's time in this world is short, and there was a lot to learn - in time his studies shifted from sparing all life towards delaying the inevitable end of his. Where science and medicine failed him, cackling hags and eldritch bargains made concessions he could live with. Now living on borrowed time he seeks out artifacts and ancients that might expand his understanding of the coming cataclysm, funding his escapades by with the occasional robbery and the odd act of folktale myth-making. Rock Plumage is not a well known name, but you may know him by another - the CelestiEarl! No? Come on, man. Anyway, he must harness his knowledge of the stars, bend them to his will and maybe, just maybe, prevent the apocalypse.
There is the added complication that he was born to a human earthling mother following her whirlwind affair with the Beholder who ran a haunted rollercoaster at the travelling fairground that came to town one summer, stealing him from her in infancy to be raised in a more traditional fantasy environment, but we don't talk about that.