There is almost no concrete information known about Spartan-312, other than the fact that, as a Spartan-III, it is likely that 312 is a war orphan whose parents were killed by the Covenant, as that is the target population the UNSC looks through for potential candidates. 312 is portrayed as a "lone wolf" assassin whose known past, covered in black ink and regarded as extremely classified, indicates extreme proficiency in combat, being rated "Hyper-lethal". In the Meet Noble Team trailer, Dr. Catherine Halsey commented that there is only one other Spartan with that classification, with the implication being that the other is Spartan-117, better known as the Master Chief, the protagonist of the main Halo games. It is also known that 312 is a talented combat pilot, and that at some point prior to the Fall of Reach, participated in a secret operation to test out the Sabre, a new UNSC space superiority fighter. Although 312 prefers working alone, the Spartan still takes the challenge of joining Noble Team with fellow Spartans Carter, Jorge, Jun, Kat, and Emile, taking on the callsign "Noble Six", the name the character is far better known by.
On July 24th, 2552, Spartan-312 was deployed to the planet Reach and officially assigned to Noble Team, with the callsign "Noble Six", replacing the previous Noble Six, Thom-293, who had sacrificed himself in order to complete a mission several weeks earlier. Moments after his arrival at Noble's base camp, the team was sent to investigate the sudden loss of communications with Visegrad Relay Station, with Reach Command operating under the assumption that it was part of a plot by Insurrectionists to steal a UNSC transport full of supplies, as had occurred on another UNSC world recently. Upon arrival at the Relay Station, however, Noble Team quickly discovered that the local farmers, as well as a squad of Army Troopers sent in before Noble to investigate the blackout, had been massacred by a small force of Covenant soldiers. The Spartans retook the Relay Station and tech expert Kat-320, Noble Two, got the system operational again, whereupon Noble One, Carter-259, contacted UNSC Central Command and activated the Winter Contingency: a plan to be put into operation in case Reach was invaded by the Covenant.
In the days that followed, Noble Six undertook many missions against the invading aliens, including an operation to retake Sword Base, an important intelligence gathering station for the Office of Naval Intelligence. Six and Kat were sent to reactivate an anti-air battery to make it harder for the Covenant to send in reinforcements, and a communications array, so that they could contact central command during the operation. After this, they re-grouped with the rest of Noble and cleared the installation of Covenant soldiers.
On August 11th, Six accompanied Noble Three, team sniper Jun-266, to perform reconnaissance and determine the strength of the Covenant force, which they discovered was absolutely massive. The next morning, Noble Team took part in a large UNSC assault force that took the offensive and directly engaged the invasion force. After the attack was routed, Noble took out several Covenant anti-air cannons, to allow for air cover, reinforcements, and extraction of wounded. Six and heavy weapon specialist Jorge-052, Noble Five, assaulted a Covenant Spire, a structure of unknown purpose, and were successful in eliminating its personnel and disabling the structure's shield, whereupon it was completely destroyed by the heavy frigate UNSC Grafton. However, it was quickly revealed that one of the operations of the Spire was to project a cloaking field over the Covenant supercarrier Long Night of Solace. Revealed to the UNSC and no longer having the benefit of surprise, the Solace quickly destroyed the Grafton, and Noble Team retreated from the battlefield.
On August 14th, Noble Six took part in Operation: UPPERCUT, a plan to destroy the Long Night of Solace using a "bomb" improvised from a deliberately misused Slipspace Drive Core. After Noble Team cleared the area of Covenant soldiers, Noble Six and Jorge were launched into orbit on a YSS-1000 Sabre prototype, the combat vessel Six had test piloted. Six, as well as a flight of the Navy's best fighter pilots, then helped defend orbital station Anchor 9 from an assault by Covenant Banshees, Phantoms, and Seraphs. The squadron then helped disable the Covenant corvette Ardent Prayer, which was scheduled to re-fuel from the Long Night of Solace soon afterwards. Six and Jorge, along with a battalion of Army Troopers from the UNSC Savannah, the ship that had given up her Slipspace Drive for the operation, then boarded the Ardent Prayer, with the intention of remotely detonating the "Slipspace bomb" once the Prayer was in position underneath the supercarrier. Although the Ardent Prayer's weapons operators managed to destroy the Savannah, the boarding party was still successful in wiping out the bridge commanders and putting the ship's movement on automatic, even though it cost the lives of all the Troopers. Unfortunately, the landing craft came under attack from surviving Covenant soldiers still on board; although Jorge and Six managed to defeat them, the Pelican they'd planned to use to escape had been damaged beyond use, and the remote detonation device had also been destroyed, requiring someone to manually trigger the detonation at the appropriate time. Jorge then threw Six out of the ship, to freefall back to Reach's surface, insisting that he be the one to sacrifice himself. The plan itself worked flawlessly, and the Long Night of Solace was destroyed, but mere seconds after the explosion, dozens of Covenant battleships - the rest of the invasion fleet - jumped into the system.
Noble Six survived the fall back to the ground, and walked for miles through the wilderness to return to the fight. On August 23rd, Six reached the city of New Alexandria, which was under direct attack in the Covenant invasion. The Spartan aided in the war effort wherever possible, including killing dozens of Covenant soldiers and aiding Army personnel in evacuating the civilian population of the city. After re-establishing contact with Noble Team, Six took part in assorted missions around the city, including the destruction of Covenant jamming devices that were preventing UNSC personnel from contacting each other, and aiding Gunnery Sergeant Edward Buck, whose squad of Orbital Drop Shock Troopers was pinned down by heavy Covenant opposition. After re-uniting with Noble Team, Six informed them of Jorge's death, and then was present when the team received a new mission, to destroy the previously re-taken Sword Base, so that its information would not fall into Covenant hands. As the Covenant fleet had begun to glass the city of New Alexandria, Noble Team then retreated to a shielded bunker, and Kat was killed by a Covenant sniper along the way.
On August 29th, the glassing of New Alexandria had finished, and the remaining members of Noble Team made their way to Sword Base, where they were redirected to a hidden underground facility and met Dr. Catherine Halsey. Halsey revealed a massive Forerunner artifact buried deep beneath Reach's surface, and that the AI Cortana had been downloading a massive amount of information stored on it into her personal memory. Dr. Halsey fervently believed that the information in Cortana's database would mean the difference between victory in the Human-Covenant War or the extinction of the Human species. Noble Team defended her lab from Covenant attackers while the last of the information finished downloading, and Cortana was downloaded into a special container codenamed "the Package", which was personally granted to Noble Six for safekeeping. Jun was assigned to escort Dr. Halsey to safety, while the remainder of Noble Team was sent to rendezvous with the last ship leaving the planet, the battle cruiser UNSC Pillar of Autumn.
Noble Team then made their way to the Aszod Shipping Yard, with Six and close-quarters expert Emile-239, Noble Four, proceeding on foot while a mortally injured Carter covered them from the air in a Pelican, later sacrificing himself by making a kamikaze run into a Scarab that threatened Six and Emile, who then fought their way through the occupied shipping yards. Upon arrival at the designated extraction point, Noble Six engaged Covenant footsoldiers while Emile operated a Magnetic Accelerator Cannon to fight off incoming ships. Once they had successfully cleared the landing zone, a Pelican arrived, and Noble Six handed off the Package to the Autumn's commanding officer, Captain Jacob Keyes. Keyes asked Six to come with them back to the Autumn, but at that moment, Emile was killed by ambushing Covenant Elites, and a Covenant battleship was approaching the shipping yards; the Autumn would not be able to take off before being destroyed unless someone stayed behind to fend off the incoming ship with the MAC cannon. Six stayed behind, knowing the Autumn was the last chance to leave the planet alive, and used the cannon to damage the battleship's glassing laser, buying the Pillar of Autumn enough time to take off and escape Reach, with Cortana using the information gleaned from the Forerunner artifact to "coincidentally" make a slipspace jump to the Forerunner installation known as Halo, leading directly to the beginning of Halo: Combat Evolved.
Alone on Reach without any way to escape, Noble Six was eventually beaten down and killed by Covenant forces, but not before taking many of them down; the squad that finally brought the Spartan down consisted of no less than seven Elites, the last of whom finally ran Six through with his Plasma Sword. Spartan-312, Noble Six, died on August 30th, 2552.
The epilogue of Halo: Reach consists of a eulogy for Noble Six read by Catherine Halsey at some point in 2589, long after Halo 3 takes place. In the eulogy, Halsey pins the Human victory in the war on Six's "passing of the torch", allowing for the discovery of Halo and the survival of the Master Chief, who was more or less single-handedly responsible for the ultimate outcome of the war. For this, she honours the Spartan's memory:
"Your body, your armour—all burned and turned to glass. Everything... except your courage. That, you gave to us. And with it, we can rebuild."
Upon starting Halo: Reach, players are prompted to customize their own Noble Six, starting with gender. This will effect Six's appearance to a degree, as well as provide either a male or female voice actor for Campaign. After selecting a gender, the player is then given an allotted amount of credits to customize their Spartan's armor, though most options are locked at the beginning of the game. Different iterations of armor become unlocked as the player progresses through the ranks and completes the Campaign. The customization screen can be accessed at any point while not in a game, allowing players to change their armor layout and colour scheme or gender on the fly.
For the single player campaign, the male Noble Six is voiced by Philip Anthony-Rodriguez, and the female by Amanda Phillipson.
In addition to visual customization, the player is also able to pick a separate voice that is used exclusively in Firefight. The cast includes a small array of characters that span the Halo universe, consisting of the following.
- Noble Six: The default voice of the Spartan. This voice is affected by the player's gender choice, but in Firefight consists entirely of combat grunts and cries, and the occasional chuckle. "Yes, sir!"
- Jorge S-052: Noble Five. Carter may be the boss, but Jorge is a living, breathing death threat. Nobody messes with Jorge. "You Model-IIIs sure get issued a nice set of armor."
- Jun S-266: Noble Three. The sniper. Good Shot. Talks too much. "I kill the enemy, but do not hate them."
- Emile S-239: Noble Four. He may say that what he wants is to win the war, but what he really wants is for the enemy to die. "Yeah, I carved that myself... I'm very proud of it."
- Kat S-320: Noble Two. The techie. Slick. Smart. She puts everything she's got and more into the fight. "It's the arm, isn't it? Don't worry, it won't be a liability."
- Auntie Dot [A.I]: The guiding A.I. in Reach. "Detecting increased aggression levels."
- Carter S-259: Noble One. The boss. He knows what it's gonna take to get this done. "We got a job to do here."
- Gunnery Sergeant Pete Stacker: A long standing soldier with the UNSC, and a minor character in every game in the Halo franchise. "I can see myself in your visor! ...Pretty."
- Gunnery Sergeant Edward Buck: Truly, if he was any better, he'd be a Spartan. "Yeah, well. Here I am."
- Sergeant Major Avery Johnson: He knows what the ladies like. "Son, I could have been your daddy, but... nah, never mind."
- Cortana [A.I.]: Fortunately, she LIKES crazy. "I DO know how to pick 'em."
- Master Chief Petty Officer John S-117: Thought he'd try shooting his way out, mix things up a little. "Didja... miss me?"