Which Assassin's Creed game introduced the Spartan warrior Kassandra as a playable protagonist?

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

Kassandra is a Spartan misthios, or mercenary, whose story unfolds during the Peloponnesian War. The game allows players to choose Kassandra or Alexios at the beginning, but Ubisoft identified Kassandra as the canonical protagonist in associated story material.

Odyssey was released in 2018 and is set in ancient Greece, beginning in 431 BCE. It expands the role-playing structure introduced in Origins with dialogue choices, branching quests, romance options, naval exploration, and multiple possible story outcomes. The game is sometimes confused with Origins because both feature ancient-world settings and a large explorable map. Origins, however, follows Bayek of Siwa and is set in Ptolemaic Egypt, while Odyssey centers on a Spartan mercenary and the Greek world.