This stuff is taken straight from the Halo Story Page at HBO.
First, on our friend the Master Chief:
"The Master Chief is the sole Spartan to leave the Reach system aboard the Pillar of Autumn (with the exception of Linda-058 in cryo). For all he knows, he is the last Spartan alive. All of humanity depends on him, for the Covenant are still strong, and there are new enemies and variables to contend with that Earth knows nothing about-the Flood, the Forerunner, and their creations, such as 343 Guilty Spark.
He has lived most of his life in various military camps on Reach; stolen from his family at six, his name changed to "John-117," his entire upbringing has been centred 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 actions, he 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." (FoR, p.6)
He is an unconventional Hero, for though he is strong, fast, and brilliant he is the epitome of none, and is surpassed by other Spartans in each area. What John does possess above all is leadership and, to both Cortana's repeated salvation and bewilderment, probability defying luck."
OK, sensible enough, but all that really tells us is that he's a SPARTAN. Now onto spartans:
"The modern Spartan program (in contrast to its ancient Greek counterpart) was initiated in 2491, an element of the ORION project. Though not much is known about the first generation of warriors (their training, augmentation, goals, etc.), they were successful enough to garner the necessary consent for a second phase, aptly named SPARTAN II. Under Dr. Halsey, the Spartans would be developed in conjunction with the MJOLNIR armour project, the culmination of a powered exoskeleton technology that had been used for some time by the UNSC, and eventually, by frustrated cargo handlers everywhere. The initial goal of the SPARTAN/MJOLNIR project was to provide a surgical strike team capable of dealing with Human rebellions quickly and efficiently, averting the use of large scale military force, and preventing the tremendous loss of life and civil war that would have inevitably ensued.
A total of 75 children, approximately age six and selected for their specific genetic dispositions (that is, being as close to perfect as science could determine), were "recruited". They were replaced with congenitally defective flash-clones to cover the enlistment, and trained, primarily on and below the surface of Reach, by one Chief Petty Officer Mendez, arguably the best Drill Instructor in the Navy. Their family names, whatever they may have been, were stripped, purged from record, and forever replaced with a 3 digit designation. Their upbringing would be defined not only by gruelling physical routine, but by a comprehensive academic tutelage under Deja, a Class II AI created specifically for the SPARTAN II project.
In March of 2525, on the orbital ONI Medical Facility above Reach, the then 14 year old candidates underwent a series of drastic and inadvisable operations to dramatically enhance their skeletal, muscular, optical, and nervous systems (FoR p.56). Of the original 75, a reported 33 survived the processes; 30 were lost, and 12 irrevocably crippled (though still used by ONI in research and ops planning).
Both before and after their final union with the MJOLNIR armour, the SPARTAN II's, with their overwhelming physical abilities, improvisational skills, and keenness for adversity, handled their operations with a profound efficiency: as of August 27, 2552 they had suffered only 3 KIA's and 1 too wounded to continue active duty, giving them the best record of any UNSC unit. Of course, they were officially listed as MIA, part of ONI Section 2's successful propaganda campaign to boost morale; a program spearheaded by the SPARTAN II's and their glorious triumphs in battle, though strangely silent concerning Humanity's slow and imminent loss of the war against the Covenant."
OK, That third paragraph (In March of 2525...) sates that the spartans underwent "a series of drastic and inadvisable operations to dramatically enhance their skeletal, muscular, optical, and nervous systems." This seems to indicate some sort of bio-organic/cybernetic implants were infused with the young spartens. The last paragraph also states that the spartens underwent a "union" with the mjolnir armor. This seems to suggest that the spartans were somehow "bonded" with their armor. Perhaps a implant chip into the brain? Weather or not all this makes the master chief a cyborg or not, I don't know, and I am to lazy to do further research on the subject.
