From the Halo 2 Manual (Human Version):Spartan 117, the Master Chief, is a member of the SPARTAN-II project. He is a genetically, biologically, and technically enhanced fighting unit, standing seven feet tall and weighing half a ton in his armor. His reflexes are unmatched, his strength and endurance quite unlike any other human and his tenacity molded by a lifetime of conscripted military training. The Master Chief is proficient in all currentballistic weapons and tactics, incursion, and unarmed combat,and has extensive experience with Covenant military tech.
The Master Chief is back in Halo 2, again the main character, and your alter ego. For details about why you are STILL badass, you are advised to read The Fall of Reach, the Halo prequel novel by Eric Nylund, and The Flood, the story of the Master Chief's battle on Halo. You were raised from a young age to be a soldier and augmented with advanced technology to make you stronger, faster, and smarter. Then, after years of training, you were outfitted with a Mjolnir suit of armor, equipped with a neural interface and a layer of crystal that can support a starship-grade AI if necessary. In short, you're still the biggest, baddest armored Covenant-smacker in all of human/Covenant/Forerunner territory.
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