Kassandra is the canonically confirmed player character in Assassin’s Creed Odyssey.
Released in 2018, Odyssey lets players choose between Kassandra and Alexios at the beginning of the game. Both can be selected as the playable mercenary, but the official novelization identifies Kassandra as the canonical protagonist for the game’s story.
Odyssey is set in ancient Greece during the Peloponnesian War, beginning in 431 BCE. Kassandra is a descendant of the Spartan king Leonidas I and becomes involved in a family conflict, the Cult of Kosmos, and the wider world of the Isu. The game includes Athens, Sparta, the Aegean islands, and other Greek regions.
Because Alexios is a complete playable option, some summaries describe the protagonist simply as “Alexios or Kassandra.” That is accurate for player choice but does not answer the canon question. Kassandra is also connected to later franchise lore through the Staff of Hermes Trismegistus.