Which Assassin's Creed game introduced the Hidden Ones as the forerunners of the Assassins?

Assassin's Creed Origins introduced the Hidden Ones as the forerunners of the Assassins.

The Hidden Ones are founded by Bayek of Siwa and Aya near the end of Origins. Their organization develops from a personal response to political violence into a disciplined movement devoted to opposing control and protecting people's freedom. The later Assassin Brotherhood grows from this early group.

Assassin's Creed Origins was released in 2017 and is set mainly in Ptolemaic Egypt during the first century BCE. Bayek, a Medjay, and Aya investigate the people behind the murder of their son and become involved in the conflict that eventually produces the Hidden Ones. The story also features the Roman expansion into Egypt.

The Hidden Ones are not the same as the Order of the Ancients, which serves as their principal enemy in the game. The later name “Assassins” belongs to a historical development that the series depicts across subsequent periods, including the Abbasid setting of Mirage.