Which Assassin's Creed game introduced the Cult of Kosmos as its central enemy faction?

Assassin's Creed Odyssey introduced the Cult of Kosmos as its central enemy faction.

The Cult of Kosmos is a secretive organization that manipulates political affairs across the Greek world during the Peloponnesian War. Players track and eliminate its members through a branching investigation system, gradually revealing the group's hierarchy and influence.

Odyssey is set in ancient Greece during the fifth century BCE and was released in 2018. Its playable mercenary can be Kassandra or Alexios, depending on the player's selection, while the Cult investigation remains a major part of the story regardless of that choice.

The Cult of Kosmos should not be confused with the Order of the Ancients in Assassin's Creed Origins or the Order of the Ancients in Assassin's Creed Valhalla. Those factions belong to different games and historical periods. Odyssey also includes the First Civilization's mythology, but the Cult is the game's principal human conspiracy.