Overdeity
Lord Ao is the Overdeity of the Forgotten Realms. He alone can allow new deities to join the pantheons of Forgotten Realms. However, he does not have mortal worshippers or grant spells, interacting with mortals only during the most unusual of circumstances, such as the Time of Troubles. However, it is made clear that even Lord Ao has his own master at the end of The Avatar Series.
Read more about this topic: List Of Forgotten Realms Deities