Kassandra is the canonical protagonist of Assassin's Creed Odyssey according to the series' later canon.
Odyssey lets the player choose between Kassandra and her younger brother Alexios as the playable sibling. The game's branching structure accommodates either choice during play, but the official novelization identifies Kassandra as the protagonist whose story is canon.
Kassandra is a Spartan misthios who travels across the Greek world during the Peloponnesian War. Her adventure includes encounters with historical figures such as Pericles, Socrates, and Alcibiades, as well as the family conflict involving Myrrine and Nikolaos.
The game is set in the fifth century BCE and takes place before the formation of the Assassin Brotherhood shown in later historical periods. This is why Odyssey explores precursor groups and artifacts rather than presenting the established Brotherhood in its familiar form.