Which Assassin's Creed game first introduced the ancient Greek setting of the Peloponnesian War?

Assassin's Creed Odyssey first introduced the series' ancient Greek setting of the Peloponnesian War.

Released in 2018, Odyssey is set in the fifth century BCE during the conflict between Athens and Sparta. Players control a mercenary from the Spartan royal bloodline and travel through regions of the Greek world, including Attica, Lakonia, and the Aegean islands.

Assassin's Creed Origins came earlier and focuses on Ptolemaic Egypt, while Valhalla centers on Viking-era England and Norway. Odyssey is also notable for giving players a choice between two sibling protagonists at the start, though the game's canon identifies one specific sibling as the central figure.