Kastor is the son of Arkantos. He wanted to go with his dad to find and punish Kamos. But his dad declined.

In Age of Mythology Titans Expansion, there is a new, shorter campaign branching off Arkantos's campaign. Kastor is mislead by Kronny pretending to be Krios and goes to fight the Greeks, Egyptians, and Norse, weakening the gods, and allowing the Titans to escape Tartarus.