The Hidden Ones were the fictional predecessor organization to the Assassins in Assassin's Creed Origins.
The Hidden Ones are founded by Bayek and Aya in 47 BCE, after their experiences expose the danger posed by secret political power. Their purpose is to protect ordinary people and oppose those who use authority to control society. The organization operates covertly and adopts principles that anticipate the later Assassin Brotherhood.
Origins is set centuries before Altaïr's Levantine Brotherhood. This chronology makes the Hidden Ones an origin-stage group rather than a separate modern faction. The game shows the organization developing rituals, hidden bases, and symbolic practices that later become recognizable Assassin traditions.
The Order of Ancients is a different group: it is the secretive organization opposed by Bayek and Aya. That distinction is important because both names belong to the same historical period. The Hidden Ones are the protagonists' organization, while the Order of Ancients represents their enemies.