Senu is the name of Bayek of Siwa's eagle in Assassin's Creed Origins.
Bayek uses Senu to scout locations, mark enemies, identify resources, and survey the landscape from above. This expands the series' reconnaissance mechanics beyond the earlier viewpoint towers and gives the player a bird's-eye view of ancient Egypt.
Senu is not the protagonist: Bayek is the playable Medjay whose investigation helps establish the origins of the Hidden Ones, the organization that later becomes associated with the Assassin Brotherhood. The eagle's scouting role also reflects Bayek's profession and the game's emphasis on exploration.
Other Assassin's Creed protagonists have different bird companions. Kassandra or Alexios can use Ikaros in Odyssey, while Eivor uses Synin in Valhalla. These names are easy to confuse because the games use similar aerial scouting systems.