Entropy

Entropy was a primordial, who was for a time and aspect of Tiamat.

History
When Ao banished the primordials to Abeir he imprisoned Entropy in the form of a sphere of annihilation and placed him on Toril as a warning to the gods that they faced annihilation if they did not behave.

In 1346 DR, Entropy got a following in Chessenta when a sphere of annihilation appeared in House Karanok's torture chamber and annihilated the wizard they were torturing there. House Karanok started worshipping it and by 1370 DR, Tiamat took the aspect of Entropy and the sphere didn't only create five smaller ones, but actually started to grant spells.

With Mystra's death and the subsequent Spellplague, Entropy was freed from his prison and grew stronger, threatening to devour the universe. He was worshiped in Chessenta by the Cult of Entropy and dwelt in the Maw of the God Swallower in southern Chessenta in 1479 DR.

Notable followers
a special type of clerics of Entropy, who specialize in the usage of a sphere of annihilation.
 * Entropist: