The Hidden Ones are the fictional precursor organisation to the Assassins in Assassin's Creed lore.
Assassin's Creed Origins shows the formation of the Hidden Ones in the first century BCE. Bayek of Siwa and Aya establish the organisation after becoming involved in a struggle against the Order of Ancients, an early form of the Templar-aligned movement. The Hidden Ones adopt principles and practices that later develop into the Assassin Brotherhood.
The organisation operates in secrecy and opposes domination by powerful rulers and conspiratorial groups. Its members use hidden blades, investigation, and covert action, linking Origins to the traditions seen in later games. The name “Assassins” is therefore not the organisation's earliest in-universe label. The modern Brotherhood develops over many centuries, and the exact terminology differs between historical periods and regional branches.