In Assassin's Creed Origins, the protagonist who becomes an early Assassin is Bayek of Siwa.
Bayek is a Medjay, a protector and lawkeeper from the Siwa Oasis in Ptolemaic Egypt. The game follows his investigation into the forces responsible for personal tragedy and political violence. His search gradually leads to the formation of the Hidden Ones, the organization that later develops into the Assassin Brotherhood.
Bayek's wife, Aya, is a major character and an important founder of the Hidden Ones. Because she is central to the origin story, some players mistakenly name her as the sole protagonist. The game, however, primarily follows Bayek and is structured around his perspective.
Senu, Bayek's eagle, helps him scout locations but is not the human protagonist. Kassandra belongs to Assassin's Creed Odyssey, which is set earlier in ancient Greece and has a separate story.