The organization later known as the Assassin Brotherhood is originally called the Hidden Ones in Assassin's Creed Origins.
Bayek and Aya establish the Hidden Ones during the story of Origins. Their aim is to oppose the Order of Ancients, a secretive group seeking political control through powerful rulers and institutions in the ancient world.
Origins is set centuries before the medieval Assassin Brotherhood seen in the first game. The Hidden Ones operate according to principles that become recognizable across the franchise: protecting ordinary people, resisting tyranny, and working from secrecy rather than openly ruling.
The name is easy to confuse with the Order of Ancients, which is the rival organization in Origins. It is also distinct from the Levantine Brotherhood, the medieval group associated with Altaïr. Later historical developments eventually lead the Hidden Ones toward the organization commonly called the Assassins.