The Realm of Atlos
Tiamat is the five-headed queen of the evil chromatic dragons. She has one head for each customary color of chromatic dragon (black, blue, green, red, white), and each head has the powers of a member of the respective race of dragonkind.
Her body is a blending of various chromatic dragon forms with an appropriately multicolored hide. Her body also has traits in common with a wyvern, including a long tail tipped with a poisonous stinger.
She was the first deity to find a way into the Realm of Atlos, but was followed closely by her brother, Bahamut.