The original name of the Assassin Brotherhood in Assassin’s Creed Origins is the Hidden Ones.
Origins depicts the formation of the Hidden Ones in first-century BCE Egypt. Bayek of Siwa and Aya create the organization after confronting the Order of the Ancients, a secretive group seeking political influence and control. The Hidden Ones adopt principles and practices that later develop into the Assassin Brotherhood seen in other games.
The title “Assassins” is therefore not the organization’s earliest name within the series chronology. Origins is designed as a foundational story, showing how a small group evolves into a wider movement committed to protecting people from oppressive power.
The Order of the Ancients is the opposing organization in Origins and later becomes connected to the Templars. “Order of Assassins” is a tempting answer because it describes the later institution, but it is not the original name used for Bayek and Aya’s group. Origins was released in 2017 and is set mainly in Ptolemaic Egypt.