Kassandra is the canon protagonist of Assassin's Creed Odyssey.
Odyssey lets players choose to play as either Kassandra or Alexios, siblings from Sparta. Ubisoft's tie-in novel and later series material establish Kassandra as the canonical protagonist, while Alexios can still be selected as the playable character in the game itself.
The story follows Kassandra during the Peloponnesian War in the fifth century BCE. She becomes a mercenary, investigates her family's past, and encounters major figures and factions from ancient Greek history and mythology.
This dual-choice system can cause confusion because both characters appear in the game and the selected character is treated as the hero during normal play. Kassandra's canonical status refers to the wider official continuity, not to a restriction on the player's in-game choice.