Final answer:
Marduk is the chief deity responsible for defeating Tiamat in the Babylonian creation text.
Step-by-step explanation:
The chief deity responsible for defeating Tiamat in the Babylonian creation text is Marduk. During Hammurabi's dynasty, Marduk was elevated to the highest tier of the pantheon and accepted as the patron god of Babylonia. Marduk was a powerful god who played a crucial role in defeating Tiamat and establishing order in the universe.