You Play the mysterious John, known as Spartan-117 and The Master Cheif, a Master Cheif Petty Officer in the United Nations Space Corp of the 26th Century. You are the last of a genetically enhanced group of super-soldiers of the Spartan II project. As the last of these super soldiers you alone wear The Mjolnir enhanced suit that increases your physical prowess through motor assistance. You are hastily removed from a Cryogenic freezer one day to find that the ship you have been traveling through space on, the Pillar of Autumn, is under attack from the Covenant (A conglomerate of several species of extra-terrestrials who have declared war on the Human race after their first inter-galactic settlement was formed) and you have been summoned by the Captain. Upon reaching the office you accept a pistol and an AI program, and are tasked with the protection of the AI because it knows the location of Earth. After battling through the ship and leaving in an escape pod you land on a mysterious ring world. After many days on the ring world you find that the planet is infested with another species of alien and must set upon a mammoth task to destroy the planet to protect the galaxy...