The female playable protagonist in Assassin's Creed Odyssey is Kassandra.
Odyssey lets the player choose between Kassandra and Alexios as the central character. The selected hero becomes the canonical protagonist in the game's later official story materials, with Kassandra identified as the canon choice.
Kassandra is a mercenary descended from the Spartan king Leonidas I. Her adventure takes place during the Peloponnesian War in the 5th century BCE and ranges across the Greek world, including Athens, Sparta, and numerous Aegean islands.
The choice can cause confusion because Alexios remains fully playable and is used as the opposing character when Kassandra is selected. That makes both names familiar to players, but the female option's canonical name is Kassandra.