Tolkien states, “when all was darkness and a great void, there was an omniscient being who lived in the vast emptiness. He was called Eru, the one, but the elves would later go on to name him Ilúvatar”
This is the being that Tolkien conceived to be the source of all creation. In the book “Ainulindalë” the first book in the Silmarillion, Tolkien outlines that the elemental thoughts of Ilúvatar became the race of gods named the Ainur, and through the power of his spirit he gave the Ainur eternal life.
If I’m not wrong, Sauron is one of the Ainur just of a lesser class which makes him a Maia. Do we know of any beings who walk Middle-Earth after the end of the third-age (after the ring was cast into Mount Doom) or do we know of how many existed?