Luminous being

The luminous being, also known as the shining one, was a mysterious entity that existed beyond the normal cosmology, at the beginning and the end of time simultaneously, yet outside time and space proper.

Description
The luminous being was a cold and harsh entity, yet at the same time forgiving and warm.

Lore
Little was known about the luminous being. It was in charge of the creation and destruction of all the universes, and the overgods, including the overgod of Realmspace, Ao, seemed to be its subordinates. Yet, around 1479 DR, it was claimed that Lord Ao served no one.

Trivia
Troy Denning, the author of Waterdeep, the third book in the Avatar Trilogy, stated on Twitter that the identity of the Luminous Being was purposefully left open to interpretation.