Which Assassin's Creed game introduced the Assassin Brotherhood's first known organization, the Hidden Ones?

Assassin's Creed Origins introduced the Hidden Ones, the Assassin Brotherhood's first known organization.

Origins, released in 2017, is set in ancient Egypt during the first century BCE. Its protagonist, Bayek of Siwa, and his wife Aya establish the Hidden Ones after confronting powerful forces and recognizing the need for a dedicated network resisting domination.

The Hidden Ones are presented as the historical precursor to the later Assassin Brotherhood. The game therefore serves as an origin story for the organization's beliefs, methods, and symbolic traditions, even though the word “Assassin” is not yet used for the group in the same way.

Odyssey takes place earlier in the timeline but focuses on the Cult of Kosmos and the Isu-era background. Assassin's Creed II and Valhalla occur much later. The important distinction is that Origins introduces the organized predecessor, not merely an individual who follows similar ideals.