Brief description
John-117/Master Chief is entrusted with the AI Cortana in order to prevent the Covenant from finding the location of Earth. Cortana represents as a hologram when she talks to him. During the videogame, she stops Master Chief before he activates the Halo, because she realizes it's purpose is to destroy all life. Her and Master Chief decide to destroy the Halo, sacrificing both Covenant and UNSC forces.