In Assassin's Creed Origins, Aya helps establish the Hidden Ones in Ancient Egypt.
Aya and Bayek form the Medjay-centered partnership at the heart of Origins. After confronting the Order of the Ancients, they help create the Hidden Ones, the organization that later develops into the Assassin Brotherhood. The game's narrative therefore presents Origins as an in-universe beginning for the organized Assassin tradition.
The story takes place mainly in first-century BCE Egypt, during the reign of Cleopatra VII and the political struggles involving Julius Caesar. Rome is deeply involved in the plot, but Ancient Egypt is the civilization in which Aya and Bayek's formative conflict and the Hidden Ones' foundation occur.
The Hidden Ones are not identical in appearance or organization to the later medieval Brotherhood. Origins shows an earlier stage, including the development of symbols, methods, and rules. The game was released in 2017 and uses historical settings while adding fictional conspiracies and supernatural technology.