In Assassin's Creed Origins, the protagonist who becomes a founding Hidden One is Bayek of Siwa.
Bayek is a Medjay, a traditional protector and law enforcer in ancient Egypt. The game follows his investigation into a conspiracy threatening Egypt during the reign of Ptolemy XIII. His personal search for answers gradually develops into a wider movement opposing political control and secret manipulation.
Bayek's wife, Aya, is equally important to the story and helps shape the new brotherhood. The game presents their work as the historical origin of the Hidden Ones, the organization that later becomes known as the Assassin Brotherhood. A common mix-up is calling Bayek an Assassin throughout the entire game; that title belongs to the later organization, while Bayek begins as a Medjay.