In Assassin's Creed Origins, Bayek's occupation is Medjay.
A Medjay was originally associated with a Nubian people, but by the Ptolemaic period depicted in the game, the term referred to an elite protector or guardian serving the community and the state. Bayek is the last active Medjay of Siwa at the beginning of the story, giving him authority, responsibilities, and local connections beyond those of an ordinary soldier.
The game uses Bayek's role to connect personal duty with the larger origins of the Hidden Ones, the organization that later develops into the Assassin Brotherhood. His investigation begins after the death of his son, Khemu, and takes him across Egypt during the reign of Cleopatra and the political struggle involving Ptolemy XIII and Julius Caesar.
Medjay is often mistaken for a formal rank such as “pharaoh” or “centurion.” It is better understood here as a protectorate office and identity. The word's meaning and use changed across Egyptian history, which is why the game's historical setting matters.