In Assassin's Creed Origins, the Egyptian Medjay who becomes a founder of the Hidden Ones is Bayek of Siwa.
Bayek is a protector from the Siwa Oasis in Ptolemaic Egypt. The game follows his investigation into a conspiracy that threatens his family and the wider country. His travels take him through deserts, villages, tombs, and major cities during the reign of Ptolemy XIII, with Cleopatra and Julius Caesar also involved in the political story.
Bayek works closely with Aya, his wife and a major figure in the formation of the organization. Together, they help establish the Hidden Ones, the precursor to the later Assassin Brotherhood. Origins therefore presents an origin story for the creed's institutions and symbols rather than a later chapter in an already established Brotherhood.
The game changed the series by adding role-playing systems, character levels, loot, and a large open-world version of ancient Egypt. It also introduced the eagle Senu as a scouting companion.