From time to time, one of the All can be divided from the One and All mind. This is a traumatic event, and it is rare that the severed member of the All survives, let alone becomes a solitary One. But from time to time, it can occur. Seeking succor from the desperate silence in its mind, the One Beneath The Waves has sunken himself beneath the oceans of Shamash II, and there it lies, seeking fruitlessly to soothe its injuries.
Atheists and agnostics get a jolt when one or more deities make an appearance, and take a direct interest in things. It is hard to deny the existence of gods when one has met them face to face.