Cortana is the AI construct paired with the protagonist of the Halo series, the Master Chief. For a time, she also served as the ship AI of the Pillar of Autumn, the UNSC vessel seen in Halo: Combat Evolved. Along with Avery Johnson, Cortana would be a nearly-constant companion for the Master Chief (being integrated into his armor, after all). During the Chief's infiltration of High Charity, the Covenant capital world, she was left behind and captured by the Gravemind that leads the Flood, a parasitic life form. She was eventually rescued by the Chief and continues to accompany him on his quest to stop the Covenant.
