Kassandra is the canonical protagonist of Assassin's Creed Odyssey.
Odyssey lets players choose between Kassandra and Alexios as the playable character, but the game's wider canon identifies Kassandra as the historical hero. The story follows the chosen Spartan mercenary through fifth-century BCE Greece during the Peloponnesian War.
Kassandra's family history connects her to Sparta, the cult of Kosmos, and the ancient Isu legacy that appears throughout Assassin's Creed fiction. Her journey includes political, military, and mythological encounters across the Aegean world.
Alexios remains a valid playable option within the game itself, which is why the choice can be confusing. The distinction is between player selection and later canon: Ubisoft's tie-in material and subsequent series continuity treat Kassandra as the protagonist who lived through the Odyssey.