Tiamat
An elemental Fiend, representing the Element of Wind; one of the Divine Progeny of the Six Dragon Gods, and a sibling of the One Dragon God worshipped in the Dragonneth faith. During the Great War, she was one of the Elemental Fiends employed as a minion by Chaos.
In appearance, she resembles an enormous, black-scaled dragon with five heads. Being that she is a Wind Elemental, her heads are known to spout various lightning-, gas- and wind-based breath weapon effects, though as a quasi-divine sponsor of evil Dragons she is known at times to conjure spells and breaths of other elements (including fire, ice and acid, among others). She is known to be both sister and rival to Bahamut.
Tiamat figures heavily into the thus-far unrealized prophesies of a "Shadow Dimension," which most people by now think is only so much Dark God bluster.