Which Assassin's Creed game introduced the Greek mercenary Kassandra as a playable protagonist?

Assassin's Creed Odyssey introduced Kassandra as a playable protagonist.

Kassandra is a Spartan mercenary whose story unfolds during the Peloponnesian War in fifth-century BCE Greece. Players can also choose Alexios, so Kassandra is a selectable protagonist rather than the only playable character. The narrative includes family conflict, political factions, and encounters with historical figures.

Odyssey is set before the historical period of the Assassins as an organized brotherhood. Its connection to the wider series comes through precursor technology, ancient conflicts, and the mythology surrounding the Isu. This makes Odyssey different from games centered on established Assassin characters such as Ezio or Bayek.