The Hidden Ones are the organization that later becomes the Assassin Brotherhood in Assassin's Creed Origins.
Bayek and Aya establish the Hidden Ones in the first century BCE after opposing the Order of the Ancients, a secret organization manipulating political power in ancient Egypt. The new group adopts principles of secrecy, resistance to tyranny, and service to ordinary people.
Origins therefore depicts the institutional beginning of the Assassin tradition rather than merely showing an individual Assassin at work. The Hidden Ones use hidden blades and operate from concealed bases, but their methods and symbols develop over time.
The Order of the Ancients is the opposing organization in Origins and is connected to the later Templar Order. The modern name Assassin Brotherhood is not the group's original name in this game.