Tiamet

Also known as the Daughter of Kyber, Tiamat embodies the evil that lurks in the heart of every dragon and she has the power to corrupt dragons. Chromatic dragons are especially vunerable to her wiles, but any dragon can fall prey to her manipulation. During the Age of Demons, Tiamat was bound below Argonnessen. 
Tiamet has her cult - known as the Talons of Tiamet - works independently of the Lords of Dust.
She stirs in Avernus where she rouses the dark emotions in the hearts of dragonkind.