Which Assassin's Creed game introduced Kassandra and Alexios as playable mercenaries in ancient Greece?

Assassin's Creed Odyssey introduced Kassandra and Alexios as playable mercenaries in ancient Greece.

Released in 2018, Odyssey is set during the Peloponnesian War in the 5th century BCE. Players choose either Kassandra or Alexios as the protagonist; the other becomes an important character in the story. The game presents the hero as a descendant of the Spartan king Leonidas and a wandering mercenary drawn into conflicts involving Athens, Sparta, the Cult of Kosmos, and the First Civilization.

Odyssey expanded the series' role-playing systems with dialogue choices, branching quests, equipment rarity, ability upgrades, and multiple possible outcomes. It also features naval travel across the Aegean Sea and visits to locations associated with classical Greece, including Athens, Sparta, and the island of Kephallonia.

Origins is the preceding main entry and stars Bayek of Siwa in Ptolemaic Egypt. Valhalla follows Eivor in Viking-era England, while Mirage follows Basim in 9th-century Baghdad. Those games share the franchise but have different protagonists and historical settings.