An UNSC Artificial Intelligence and one of the greatest assets in humanity's war of survival, Cortana is as close to a person as a computer program could become, though she has no true physical form. Recovered by the Master Chief from the Flood infested Covenant warship High Charity, Cortana is once again the Chief's companion and confidant, the closest thing to a friend he has. Trusting in each other, they face the threat of the Flood and the Ark together.