The Master Chief, ranked as Master Chief Petty Officer of the Navy, known with his real name and assigned number, John-117 is a commando of the UNSC and one of the recombinant of the SPARTAN-II project. He is a highly-ranked, obscure, genetically-altered super soldier bred for war, serving as humanity's last hope in the lethal conflict against the Covenant. The Master Chief, also known as Spartan-117, or simply John, is a creation of the mysterious SPARTAN-II project. Outfitted with the ability-enhancing MJOLNIR MARK VI battle armor and heavily trained for combat with an exceedingly diverse array of weaponry, John-117 is a force to be reckoned with. All Spartans stand 7 feet tall, and in their armor weigh over half a ton.
The Master Chief is the main protagonist in Halo: Combat Evolved, Halo 2 and Halo 3. He is one of the last Spartan-IIs; most of the others were believed to be killed in a Covenant bombardment of the planet where they became Spartans, Reach. The Master Chief's appearance is unknown, and there are some instances of the games where it appears as though this hidden appearance is an inside joke for the developers (ie. cutscenes where we are lead to believe we will see his face but ultimately do not).
Throughout the games, the Master Chief has an almost legendary status amongst the humans, and as an ironic juxtaposition, is known as "The Demon" amongst the Covenant. In game, Covenant will sometimes say things like "I've killed the Demon" (if they kill the Master Chief) or generally utter phrases including the word "Demon". The Arbiter in Halo 2 also refers to the Chief as "the Demon" on several occasions.
 Early Years
John was born in 2511, he lived with his both parents in the Eridanus System, on a UNSC rural colony known as Eridanus II. He lived in a rural city called Elysium City, there he attended a primary school Number 119 until the age of six. At that time, the SPARTAN-II project was been initiated by the UNSC in collaboration with Dr. Catherine Elizabeth Halsey. She considered him to be a possible candidate for the program alongside other individuals, all are to be tested and studied for the SPARTAN-II project applied to super-soldiers. John himself was a "Super" kid in his age, being different than others with more mental strength and high IQ levels, he also had great physical features. In 2517, when he was six, Dr. Halsey and Captain Jacob Keyes came to visit and study John, multiple tests were done, mental ones and physical ones. John, in addition to his skillful abilities, is considered to be lucky, literary lucky. Which he denies it later on and state that "We Make Our Own Luck" to Dr. Halsey. Although he resisted, john was kidnapped alongside other seventy-four children to be Inducted to the SPARTAN-II program and were replaced by fake bots that simulated them, known as Flash Clones. John took his "John-117" name when he arrived to Reach colony with Dr.Halsey where he was informed about his role as a SPARTAN-II super soldier, and his role alongside the UNSC force to protect Humanity and its interests.
In September 24th of the same year, 2517, the master chief started his first trainings under Franklin Mendez, he met the first AI he ever saw, the Deja. The next day he befriended with Samuel and Kelly. Two years later, John earned his first recognized promotion to a Squad Leader after completing a mission in the mountains of Reach, where he was assigned as a leader by his fellow mates during the mission. He showed a clever move from him when he intendedly stayed the last one in his group to fallow, that is because anyone who is left behind must be punished and fellow mates must not give a hand. This action also showed how honored and wise he was, merits that helped him to be one of the most recognized and special SPARTAN-II project recombinant.
When he turned 14, as the case with most SPARTAN-II candidates, went through the SPARTAN-II Augmentation Procedures which improved his abilities dramatically, and he managed to pass through the deadly risks unlike most candidates, who in turn end up dead. The procedures included Carbide Ceramic Ossification which enhanced bones, Catalytic Thyroid Implant which allowed a candidate to grow rapidly and in a healthy manner, Muscular Enhancement Injections and more that enhanced the physical durability and strength of the SPARTAN-II candidates. After surviving the procedure alongside other thirty-three candidates, John was sent to Atlas carrier-type vessel where he killed two ODST officers in a fight and injured others.
 Military Career Life
After the vast extendedness in Human civilization and colonies growth to outer worlds and planets, rebels started to show up and a civil UNSC-Rebels war was streaming, rebels wanted independence from the UNSC power and other obscure desires. John first actual military mission was regarding the rebels in the Eridanus System, and capture the well known leader of the rebels, Colonel Robert Watts.
After the incidence in Harvest and the human's first encounter with the Alien unified empire, the Covenants, and after receiving his Mk IV armor, John fought his first battle with the Covenants in the Battle of Chi Ceti. John was to destroy a Covenant ship, and he alongside with his best friends Samuel and Kelly, managed to destroy the Covenant ship which resulted in the lose of Samuel after sacrificing himself.
In 2535, John made his first contact with the Arbiter when he was sent a mission to retrieve a package from the nearby Covenant fleet, discovering that the package was the kidnapped Dr. Halsey. John and the Arbiter engaged in a duel where John was almost killed, but thanks to the retreating Elite Fleet Master in charge of the Covenant ship, John made it alive and rescued Dr. Halsey. Arthur and Solomon, who were his partners in this mission, were dead, Kelly thought to be dead too until John regrouped with her back in the Ship they came from. John battled Covenants mission after mission in a series of over two hundred missions and engagements with the Covenants. He was well known for his high end skills and he received most of the medals that can be received in the UNSC.
 Fall of Reach and Flood
After the events on the Reach colony, John received his Mk V armor which was seen throughout Halo: Combat Evolved. After the battle for Reach, John retreated to the Pillar of Autumn (Human Starship) and fled away into Slipspace and into an unknown location in order to lose the Covenants , in respect to the Cole Protocol that states that no retreating Human fleet should retreat to Earth or any other major colony, that in order to prevent Covenants from invading them. After traveling through space in the Pillar of Autumn, Captain Jacob Keyes, the captain of the ship, discovered an unknown object, the Halo Installation 04.
After the Covenants reached and stroke the Pillar of Autumn, John as the Master Chief was awaken from his cryo-sleep to battle of the Covenants once again. Several lifeboats made it to Installation 04 after the crash of the Pillar of Autumn, Including John and Cortana implanted into his Helmet. After hours of searching for survivors and rescuing Keyes from the Truth and Reconciliation, John went to the Control Room of Alpha Halo to discover what it is really is. Hours later, John went to the Library of Alpha Halo and encountered the ancient nightmare, the Flood. He also encountered the Monitor 343 Guilty Spark and made a temporary alliance with him, the Monitor asked for John's aid to retrieve the Index in order to activate Halo and destroy the Flood. After fighting unimaginable waves of Floods and surviving infection, proving the extreme skill of John-117, he made it to the Index Chamber alive and retrieved the Index for the Monitor.
After returning to the Control Room with his newly made ally, John was surprised by the discovery that Cortana made, the Monitor's cause was noble but its cost is untolerated. The Monitor was about to destroy all life in galaxy again as happened centuries ago in the Forerunner-Flood War. John destroyed the Alpha Halo later on by exploding the Pillar of Autumn Fuel Rods, John made it out the Installation by flying the Longsword Fighter after he witnessed the destruction of Echo 419. Alpha Halo was destroyed and so was the Flood, as it was believed.
 Operation: FIRST STRIKE
After the destruction of the Forerunners' Alpha halo, John alongside with Cortana made it out and discovered other cyro-tubes floating in space that contains some SPARTAN-II soldiers, such as Linda. John brought extra survivors to the Longsword after distracting the Covenants' Ascendant Justice, then he went to capture the ship and travel through the Spaceslip to Reach looking for more survivors. There, John found some SPARTAN-II soldiers and Dr. Halsey, they then stopped at a Eridanus Rebels base for repair and left to the Covenant command-and-control center Unyielding Hierophant.
The Covenant figured out the Location of Earth and John with his fellow SPARTAN-II soldiers set to stop them somehow, they destroyed the Unyielding Hierophant then. The team then encountered the Brutes for the first time, and Grace, one of his fellow soldiers, fell and died. After several battles and missions, John made it back to Earth.
 Battle for Earth
After coming back to Earth, John was honored and given his new Mk VI armor, he attended the award ceremony at the Cairo Station alongside with Sergeant Johnson. The ceremony was to be done in haste, news reported the arrival of the Regret Fleet that attacked the Stations orbiting Earth, resulting in the initiation of Battle for Earth. The Covenants destroyed two stations and planted a bomb in the Cairo Station, Elites, Grunts and the newly encountered Drones invaded the station only to find death on the hand of John and his newly received armor. After deactivating the bomb by Cortana, John planted back the bomb in a Covenant Assault Carrier fusion core instead of throwing it in empty space. After planting the bomb, John made it back to the UNSC In Amber Clad.
After the Covenants made it to Earth, John was sent to New Mombasa in Africa via the UNSC In Amber Clad in order to save the city and kick out the Covenants. When he was dropping via a Pelican, John was shot down by a large and giant Covenant Scarab. John then cleared and took out many Covenants ground force and took the Scorpion to destroy the massive Scarab. After numerous engagements with what remained from the Covenant ground force, the Scarab was finally destroyed and john made it back to the UNSC In Amber Clad with a group of Marines and Miranda Keyes set to pursue the Prophet of Regret, which lead them to Installation 05 via a Spaceslip after the chase.
 Installation 05
After reaching Installation 05, John sought to kill the Prophet of Regret with the aid of other ODST individuals. The Prophet of Regret determined destruction and intended to activate the Halo. Later on High Charity ordered a Destroyer to glass out and bombard the temple, resulting in the death of The Prophet of Regret and having his body turned into a Flood form, John almost died too but because of his famous luck mixed with his unique skills he survived.
John was captured then by the Flood and sent to meet the Gravemind, who explained that both Floods and Humans want to avoid the activation of the Halo. He asked for a mutual effort to stop the Halo and ordered the Chief and Arbiter to locate the Index. The Index happens to be with the Covenants in High Charity, where the John went to. A civil war was raised that threatened the stable system of the Covenant Empire, resulting in a Loyalist Fraction and a Fraction that consists of Elites led by the Arbiter, which allied with the Humans.
Prophet of Truth fled and decided to attack Earth, this was then informed to John by the dieing Prophet of Mercy, the Covenant still have the index and they are still capable of activating Halo. Thus, John left Cortana behind for this and made his way back to Earth on the Forerunner Dreadnought.
 Defending Earth Again
After various encounters with Covenant forces and being captured and interrogated, the Master Chief was able to escape and make it back to Earth on the Forerunner Dreadnought. The Dreadnought was crashed on Earth, and the Master Chief collapsed, which in turn caused sergeant Johnson to treat him as a dead spartan. The Master Chief stood up moments later, and tried to kill the Arbiter not knowing his separation from the covenant empire alongside all Elites.
The Chief and the Arbiter with the sergeant went through the woods to search for survivors, they were captured by brutes and rescued later. They were then evacuated by a UNSC Pelican to Crow's Nest base in Kenya. The base was invaded by Covenants and the Chief was informed to defend it while survivors and marines are evacuated, plus planting a bomb to destroy the covenants and the base, then escaping in an freight elevator. He escaped with several marines through the Highway to the city of Voi in Kenya, with the base shattered and destroyed.
The Chief battled through Covenants in the Battle of Voi to reach the Artifact, thinking it was Installation 00. The chief destroyed a couple of Covenant heavy vehicles and anti-air units, allowing the UNSC frigates to shoot down Truth's Dreadnought.