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Black-One (name and Spartan tag unknown) is a SPARTAN-II supersoldier of the UNSC Naval Special Warfare Command serving under the Office of Naval Intelligence. She is the leader of Team Black, and is visually distinguished with the Roman numeral "I" on her visor.

Conscription and training
She was abducted and conscripted into the SPARTAN-II program by Dr. Catherine Halsey in 2517 when she was six years old. She was then taken to the planet Reach, and trained by the AI Déjà and CPO Mendez, along with the rest of the Spartan children.

She was assigned as the leader of Team Black, and trained with the other teams such as the Red Team. While in training, Black-One was in a secret relationship with Black-Three. Victor-101 was jealous of Three and ratted them out to Chief Mendez, who sent them both to the brig. Red Team tracked Black-One down as team leader and attacked her, claiming they weren't taking their training seriously enough. Black-One lost her left eye resisting them. Black Team later got payback, resulting in another ten days in lockup.

In 2525, she and the other candidates underwent a series of augmentations to improve their combat prowess. Black-One was among the ones that survived and were not crippled or killed by the procedure.

Raid on Verge
During the Human-Covenant War, Black-One led Team Black in various operations against the Covenant. During one of their missions, they destroyed a Covenant base facility, and in another, they boarded a Covenant cruiser using C-12 shaped charges.

In mid-2552, they were sent to destroy a Covenant Beacon in the city of Ciudad de Arias on the former UNSC colony of Verge. After landing on Verge, the team made their way past fortified anti-aircraft emplacements to the city, where the Beacon was situated. In a skyscraper, they observed a large swarm of Yanme'e, overseen by Kig-Yar and Mgalekgolo guards at the Beacon. Black-Two then found an injured, apparently non-hostile Yanme'e. The Drone, nicknamed "Hopalong", told them of an alternate, hidden route to the Beacon. While Black-One and the rest of the team were suspicious, they decided to trust the Yanme'e.

In the next morning, the team proceeded to move to the Beacon through the tunnels. The Spartans eventually reached a large cavern near the Beacon and parted ways, each heading for one of the Beacon's four anti-gravity pylons. After a ten-minute countdown was up, One ordered the rest of the team to engage the guards near the pylons and place their C-12 charges on them. Meanwhile, Hopalong had acquired a Covenant device which it used to free the rest of the Yanme'e. It was then revealed that Hopalong had tricked the Spartans: the Yanme'e, who now started attacking the Spartans and the Covenant, were actually psychopathic prisoners incapable of normal socialization with the rest of their kind.

One ordered the team to return to the rally point at the tunnel entrance, but Two discovered a better means of escape: an intact underground train. They decided to head to the train, but not before Two, against One's orders, went to rescue an injured Black-Three while One and Four regrouped at the train. While on their way to the train, Two also detonated the charges on the Beacon, destroying it. Everyone managed to get onboard and they escaped the city as the tunnels caved in under the collapsing Beacon, and headed to a Pelican dropship for exfiltration.

Line Installation 1-4
Some time after the mission on Verge, the ONI-commissioned mining vessel Long Time Coming was ordered to transport Black Team while they were in cryo-stasis. Before the ship could reach its destination, however, it was shot down and crashed on an unidentified moon. The ship's AI, Iona woke the Spartans from their slumber. Black-Two was then assigned to remain on the Long Time Coming to drop a Slipbeacon while the rest of team moved outside to investigate a nearby structure that appeared to contain breathable atmosphere. Unfortunately, they were ambushed by a group of Covenant, who had also been shot down on the moon. Both groups were then confronted by Forerunner constructs known as Gatherers, who brought Black-One and several Covenant soldiers to a Forerunner complex. Upon arrival, a Forerunner Monitor, 686 Ebullient Prism, greeted them and stated that he was going to dissect all of them to find out if any of them were immune to the Flood.

Luckily, Black-One was able to free herself and an Elite named Reff 'Talamee by using her helmet to deflect a laser at one of her ammo magazines lodged in one of the Gatherers. She then grabbed the robot's weapon to use against Ebullient Prism. Once they had avoided and blinded the Monitor, the two discovered the Installation's central control center. Accessing the console, One learned that a Covenant fleet was in proximity to the moon. She tried to contact the rest of her team but Black-Three and Victor were engaged in a brawl, having been manipulated by Prism into fighting each other. To stop this, One told Victor that she forgave him, giving Three the opening to jack in Iona's Data Crystal Chip into Victor's MJOLNIR armor, causing an influx of the team's various mission to remind Victor about his family and bring him out of his tantrum.

One was slammed into the console by a Hunter and knocked out. Reff tried defending to his brother Thon that the Spartan saved him. Thon snapped that he honored the truce he made with the Spartans only to rescue him. He then changed the subject to inquiring how to contact the holy city of High Charity. However, Reff stated that they should instead blow the servants of the Prophets out sky, believing that his kidnapping was the work of destiny. He then killed Thon when his brother attempted to kill him for speaking heresy. Reff was then vaporized by Prism. Black-One managed to recover to assist the rest of her team in stopping Prism, directing him into the path of the Installation's main gun, vaporizing the Monitor while simultaneously sending the Covenant fleet in Slipspace transit crashing down to the moon. Black Team then began to fight through the surviving Covenant to commandeer a functional Slipspace drive.

Personality and traits
As the team's leader, Black-One is not easily distraught from the mission and is always focused on the task at hand. Despite her no-nonsense leadership, she has a dry sense of humor which often manifests as occasional military banter or sarcastic remarks. She is generally calm and capable of reasoning and logical decision-making, even in the direst of situations.

List of appearances

 * Halo: Evolutions - Essential Tales of the Halo Universe
 * Blunt Instruments
 * Halo: Blood Line