The Master Peter

The Master Chief was the sole Spartan to leave the Reach system aboard the Pillar of Autumn (with the exception of Linda-058 in cryo). For all he knew, he was the last Spartan alive. All of humanity depended on him, for even after their defeat at Halo 04 the Covenant were still strong, and there were new enemies and variables to contend with that Earth knew nothing about: the Flood, the Forerunner, and their creations, such as 343 Guilty Spark.
After his whirlwind tour of Delta Halo, his introduction to a host of new "friends", and a hitch-hike back to Earth aboard a Forerunner vessel it remains only to be seen how he plans on "finishing this fight".

He has lived most of his life in various military camps on Reach; stolen from his family at age six and his name changed to "Peter-117", his entire upbringing has been centered around making him a mechanism of military efficiency, utilizing both force and tactics. He displays an odd sort of attitude for a creation of the military: he does not glorify his violent actions, but merely does what he has to do. He does not hate his enemy; he kills them because he knows it is his duty to kill them; to win. "It wasn't [the Chief's] job to make things suffer - he was just here to win battles. Whatever it took."

He is an unconventional Hero, for though he is strong, fast, and tactically brilliant, he is the epitome of none of those attributes, and is surpassed by other Spartans in each area. What Peter does possess above all is leadership and, to both Cortana's repeated salvation and bewilderment, probability-defying luck.