Fomora

Fomora, the Mother of Demons, Tiamat in Draconic, is the goddess of destruction and the embodiment of chaos. She created the Abyss and demon-kind. As the embodiment of chaos, her only goal is thought to be destruction itself.

Warm-blooded Pantheon

In the warm-blooded pantheon, depictions of Fomora are rare, as it is feared that just depicting her risks inviting her into the world. In what depictions there are, she is shown variously to be either a formless, ghostly figure or to be a colourless, robed feminine figure. It is thought that gazing upon her true form would be enough to drive one mad.
As an interloper god, Fomora did not take part in the initial Creation of Morn. Mortus thought her destructive nature was unsuited to the project of creation. Even other interloper gods were against her interfering. Fomora intervened in creation by creating her own realm, the Abyss, and demon-kind, sending them to Morn to wreak chaos and spread her influence.
Fomora's intervention in creation came after Asmodeus had given mortals selfishness. Fomora was able to use this weakness to grant another trait to mortals - violence. It is thought that it would not have been possible for her to do this had Asmodeus not made mortals selfish.

Draconic Depiction

In the Draconian pantheon, Tiamat is depicted as a multi-headed chromatic dragon. She is usually shown as having five heads with the body of a black dragon. Her wings are shown to be withered, with dark tendrils growing from their membranes.
During creation, Tiamat rose from the ancient oceans to war with Bahamut. With every step she took on land, she left a toxic footprint from which demons rose. Bahamut eventually defeated her, forcing her back beneath the ancient oceans and into the Abyss, but he lost a limb in the process.