The creation myths of Sumer and Greece share a common character named: chaos Zeus Cronos Tiamat

The answer to this is Zeus.

Tiamat

Explanation:

The Akkadian word for sea, tâmtu, is related to Greek Θάλαττα (thálatta),

The two names having become essentially the same due to association.

Reference: Burkert, Walter (1992). The Orientalizing Revolution: Near Eastern Influences on Greek Culture in the Early Archaic Age. Cambridge: Harvard University Press. pp. 92f. ISBN 0-674-64363-1.