Kassandra is the canonically featured protagonist in Assassin's Creed Odyssey.
Odyssey lets players choose between Kassandra and Alexios as the playable character, but the game's novelization and later franchise material identify Kassandra as the canon protagonist. She is a Spartan mercenary whose story unfolds during the Peloponnesian War in the fifth century BCE.
The game is set across ancient Greece and includes storylines involving Sparta, Athens, the Cult of Kosmos, and the player's family. Kassandra's choices influence relationships and outcomes, while the broad historical setting remains rooted in the conflict between Athens and Sparta.
Alexios is not simply a different unrelated hero: in the game's choice system, he takes the role not selected by the player and appears as Deimos. This is why both names are strongly associated with Odyssey. Kassandra later appears in crossover material connected with Assassin's Creed Valhalla, reinforcing her canonical status in the wider series.