Who or what was Tiamat?

Tiamat, in ancient Mesopotamian mythology, is the primordial goddess who was the personification of the salt sea and the mother of the gods. She also was associated with the chaos of creation. Tiamat and Apsu, also spelled Abzu, the personification of the fresh water beneath the earth, are the source of a family of gods with whom she eventually went to war.

She was slain by Marduk, the chief god of the city of Babylon, and from her body he created the universe. In later myths, Tiamat was sometimes portrayed as a serpent or dragon, and these images have inspired creatures in modern popular culture, notably in the role-playing game Dungeons & Dragons.