Origin
Tiamat may have been the original form of Gaea when she emerged from Chaos, she would find a mate in Aspu and together they would spawn the first gods.
Top Cow:
Tiamat was trapped by the bearers of the Witchblade and the Angelus in a crown in ancient Egypt. The crown was passed through many hands throughout the ages until a cat burglar finally stole it in New York City. When the thief placed it on her head, Tiamat took control of her body, immediately renewing her vow for vengeance against those who trapped her so long ago.
Zenescope:
He appeared once in the land between Earth and one of the other realms to test Samantha Darren.