World under revision! This world was originally written purely as a Dugeons and DragonsĀ® setting. It is (slowly) being rewritten to be system agnostic When things don't seem to work togewther, this is likely why.
There are many kinds of celestials, but they are all native to the upper planes, even if some of them have taken up residence somewhere else. The type of creature includes everything from unicorns to white winged foxes to planetars. Most celestial races are in one way or another the direct creation by a deity to aid them in their task. But since then, they might have gone their own way.
There are rare celestials that hold very special positions, making them quasi lesser deities themselves, or at least avatars of a deity. The Caliph of the Sh'areen Caliphate is one food example.