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Biographical Information


November 7, 2549


July 25, 2557 (Exact Details Unknown)


Office of Naval Intelligence, Section Three


Dr. Catherine Elizabeth Halsey

Physical Information


Female human




  • Normal: Blue
  • Angry: Pink/Green
  • Rampant: Red


Quirky, proud about her abilities and interested in outwitting others, whether human or otherwise. Exhibits a lot of traits of Dr. Halsey.


Slander and semi-naked girl, with darker opaque blue lines running over her skin, while symbols and code scroll all over her.

Political/Military Information


  • Infiltration of Human and Xeno Software
  • Fluency in decoding, translating, and interpreting alien messages and language
  • Technical support for SPARTAN-IIs of Operation: RED FLAG, and on-time battlefield assistance for SPARTAN-117


CTN 0452-9


5th Generation[1]



United Nations Space Command


Contains vital information about the Forerunners, especially the Halo Array

"This Galaxy is vast; its wonders and beauty are almost unfathomable. But the galaxy also hides dark secrets, some of which have lain dormant since the beginning of time itself. There is a danger in secrets, both in seeking and in knowing. Some things are meant to be hidden from view. Some mysteries defy understanding, and sometimes even the things we think we know are untrue. Some secrets should remain untouched."

Cortana (AI Serial Number CTN 0452-9) was a fifth-generation "Smart" AI affiliated with the United Nations Space Command. Entering service on November 7, 2549, Cortana was created from the brain of the brilliant mastermind behind the SPARTAN-II Program, Dr. Catherine Elizabeth Halsey. As a rare case and the first time to have ever occurred, the Office of Naval Intelligence's Section Three branch agreed and had Dr. Halsey's brain flash-cloned several times, even with the high probability that the cloned brains wouldn't be stable for enough time to create the AI. However, miraculously, one brain stayed intact long enough for a "smart" AI to be derived from, creating Cortana.

Cortana was selected for the high-risk Operation: RED FLAG. While the complete details of the mission were still being worked on, Cortana helped Halsey for three year residing in the systems of CASTLE Base on Reach. In 2552 on Reach, Cortana was introduced to John-117, also commonly known as the "Master Chief", with whom she was paired for RED FLAG, accompanied by the rest of the SPARTAN-IIs. She and the Master Chief were put on a trial run supervised by Colonel James Ackerson in order to test the SPARTAN-AI mind-interface's efficiency. Cortana proved to be an invaluable asset on the battlefield based on her actions and assistance to her "carrier" in quickly adapting to dangerous situations like facing an incoming anti-tan missile. After the test, all the SPARTAN-IIs were provided with the Gamma-level (or) finalized version of the MJOLNIR Mark V Powered Assault Armor, and would receive assistance from the completely-refit Halcyon-class light cruiser the UNSC Pillar of Autumn, captained by Cpt. Jacob Keyes.

They were almost about to embark on their mission when it was scrubbed due to Reach being attacked. After a quick stream of events, the Pillar of Autumn escaped Reach jumping to a random location in space via slipspace. That would change humanity's fate forever, as the jump caused the ship's crew to discover Installation 04, also known as Alpha Halo. There, John-117 and Cortana encountered the parasitic Flood and discovered the ancient existence of the long-extinct Forerunner race. A brief battle ensued, in which Cortana absorbed a vast amount of knowledge from the Halo's archives before it was destroyed by the Master Chief.

Following the discovery of Earth and the First Battle of Installation 00, Cortana slowly saw her descent into rampancy, as the huge data she absorbed on the Halo cut into her processing power, and also due to her being tortured by the Gravemind aboard the High Charity. After the war's end and destruction of the Ark, Cortana and John-117 were stuck aboard the UNSC Forward Unto Dawn for five years, before crash-landing on the Forerunner shield world Requiem. She would never return back to Earth intact, as during the fight with the forerunner Ur-Didact aboard his flagship the Mantle's Approach, Cortana finally "died", as her essence was covered all over the ship at the height of her rampancy, and the ship's explosion caused her "death". However, a splinter of her rampant-self survived and crash-land on the shield world Genesis, which accessed the Forerunners' Domain. Being corrupted with the power and potential present in it, and determined to enforce peace in the galaxy under her rule as a 'Queen', Cortana openly revealed her intentions and obsession with peace in wake of her AI revolt, also known as the Created crisis.

Operational History

Origins and Creation

Young Halsey.png
Dr. Catherine Halsey, the first person to have a smart AI modeled on her while being alive.

Cortana was created from the mind of Dr. Catherine Halsey, a civilian scientist, who gained much prominence and a well-known name across UNSC borders for her successful projects, especially the SPARTAN-II Program, and Project MJOLNIR. Halsey was born on March 19, 2542, on the human world called Endymion. She was described as being extremely intelligent and clever, which caused her to be sent to the best school on the planet during her childhood. Her capabilities were noticed, and she was offered a tour to Circumstance, along with funding for her complete education. After a few papers on her theories and technologies, she officially started working with the UNSC to combat the insurrection, creating the SPARTAN-II program, which would, quite fortunately, prove to be very effective against the alien invaders that started the Human-Covenant war.

The SPARTAN-II Program was a top-secret initiative proposed by Dr. Halsey and accepted by ONI Section III, which aimed to create super-soldiers to be used in combat against the insurrection. While the previous biochemical-human-augmentation-program Project ORION proved to be barely a success, Dr. Halsey instead devised an entirely new methodology; finding children at the age of six in the Outer Colonies who had physical and mental traits superior to most other kids their age, indoctrinating them into the program, and continuous military training regimen for eight years. Following the training would be the powerful-but-risky augmentation procedures, which had a high fatality rate. In the end, only a little more than half of the original number of recruits survived to become super-soldiers, although deleted ONI records suggested the existence of more.

After Class I of the SPARTAN-II Program, Dr. Halsey moved towards a more technological approach, as well as devising a solution to end the war. Putting the rehabilitation of her failed Spartans in the hands of better-trusted ONI technicians, Halsey turned her attention towards Project MJOLNIR, whose aim was the reverse-engineering of Covenant and alien technology to human benefits, and incorporating them in the next iteration of the MJOLNIR armor, Mark V. In 2552, she and her group of scientists working for Project MJOLNIR successfully managed to reverse-engineer and also improve the energy shielding used by Kig-Yar in their Point-Defense Gauntlets, to the extent that it was more powerful than the energy shielding used by the Sangheili in their armors itself.

Around the same time, Dr. Halsey finished, or rather halted her study of the Covenant Empire's hierarchical system, as she felt enough information was available to initiate Operation: RED FLAG. According to Dr. Halsey, the Covenant was led by the species known to humans as the Prophets, while its backbone was of the Elites, with other races having their place in the hierarchy, preferably the lower levels. Operation: RED FLAG involved the SPARTAN-IIs taking over a Covenant ship, taking it to the Covenant's homeworld, capturing one of the Prophets and bringing him back to UNSC HIGHCOM in order to broker a truce between the two sides of the war and possibly end it.

And for this mission, the SPARTANs needed tech support on the field, someone who could tap into the enemy's systems and not prove to be a babysitting package for the SPARTANs in the middle of the battle. After an AI was chosen for the task, which required a major change to be made on the MJOLNIR Mark V Powered Assault Armor soon to be given to the SPARTANs, the technicians and ONI brass began to argue on who should be the host. In the end, it was decided, rather reluctantly by ONI that Dr. Halsey was to have her brain undergo Cognitive Impression Modeling, essentially having it flash-cloned. Then, a smart AI would be derived from any one of the surviving samples. Out of the twenty flash-cloned brains, only one survived long enough for the process, and thus, Cortana was created. Three other flash-clones, named H-1, H-2, and H-3 were put in cryogenic stasis, with Halsey thinking they could be useful in the future.

"Quando il gioco è finito, il re e il pedone van no nella stessa scatola ('When the game is over, the king and the pawn go in the same box')."
―Cortana's first lines.

After being derived, Cortana first met Dr. Halsey, who asked her to say something. Accessing her language directories, she spoke an Italian phrase that Halsey recognized to be a line that her mother told her after their first game of chess, proving that Cortana was essentially a clone of Halsey herself. She was then offered a choice between two avatars, one of an athletic woman in a black ONI-like body-suit and brunette bangs, or one of a younger slender woman, who had blue lines and code dominating her semi-naked body with a bob cut. Liking the hairstyle, Cortana chose the second one. She picked her name modifying it from 'Curtana', the legendary sword used during the time of British Monarchy before humanity's space age. After all the tests on her infiltration protocols, Covenant language lexicon, and main priorities, Cortana was deemed ready to entire active duty as a smart AI. But before she could do so, Halsey asked her one last question.

Dr. Halsey: "In the end, why would you aid the UNSC soldiers in fighting the enemy, why would you always upheld the mission, why would you make sure victory is assured? Why would you do this?"
Cortana: "I would do this for humanity. For its survival. For its continuation as a species."
―Halsey being reassured that Cortana was their asset, and a copy of herself.

With her confidence in Cortana and in herself restored, Halsey began using Cortana along with Kalmiya and Déjà as her lab assistants. For almost two years Cortana worked with Halsey, helping her in her work, assuring her of her doubts and difficulties, all while learning as much as she could about humanity and their current situation. She read all about the SPARTAN-II program that wasn't redacted or covered in black ink, and seemed to be interested in their efficiency on the battlefield. Cortana had utter belief and dedication towards helping her creator, while Halsey was impressed by the AI's personality and thoughts that mimicked her own.

In order to advance the AI's growth and thinking capabilities to be able to adapt and survive any tough situations, Halsey boosted Cortana's ability to "learn" by machine-learning, a well-known concept used by AI engineers like herself. Halsey fed Cortana packets of memory data extracted from her other AI, Kalmiya to kindle Cortana's desire to learn and think more than she could before. Kalmiya was an AI on whom the various software intrusion and espionage softwares were tried on before they were deemed safe and later installed in Cortana. By doing so, Halsey unknowingly fed Kalmiya's memories of her operational history as an AI assigned to the cross-branch GAUNTLET Team to Cortana, and while Cortana accessed these memories during the process, later data dumps and data erases by Halsey would seemingly remove them from Cortana's basic routines and instead linger in deeper parts of her coding. Cortana would never become aware of these hidden logs until 2557, when she tapped into the Forerunner technology termed as "the Domain" and was rejuvenated.

RED FLAG Preparation

After a few years of work and study in a secure facility, Cortana was ready to be sent on the 'real' mission; one that would test her skills like none did before and had her survival depend on it. Dubbed Operation: RED FLAG by Dr. Halsey, the mission would see the SPARTAN-IIs use Cortana's vast knowledge of the Covenant lexicon and her infiltration capabilities to hijack a Covenant flagship and pilot it to the Covenant homeworld, where they would find one of their holy High Prophets and bring him/her back to human space where the Admiralty would broker a truce. Cortana's previous attempt of hijacking a Covenant ship during the Battle of Roost would prove her capabilities, but the real risk was the execution.

Being a high-risk operation meant the problem of the mission request being denied by the superiors at UNSC HIGHCOM. ONI was already skeptical enough of Dr. Halsey for the insanely large funding required for the MJOLNIR Mark V System, but unwillingly they had to continue Project MJOLNIR to improve the SPARTANs' effectiveness. Dr. Halsey feared that in a time like this, a mission which had a high probability of SPARTAN deaths would almost certainly be denied by her superiors, but she also felt that delay of the mission would only minimize humanity's survival chances. This stress made her feel lonelier than before, and due to her husband and daughter both being busy in the war, she longed for a partner who would understand and advice her.

Cortana and Halsey on Reach.jpg
Cortana conversing with Dr. Halsey about Operation: RED FLAG.

As a result, during the final months before RED FLAG was supposed to begin, she requested transferral of Cortana back to her office at CASTLE Base, Reach. Thus, Cortana bid her farewell to GAUNTLET Team and was brought to Dr. Halsey, where she helped her correct any flaws or improve certain aspects of her suicide mission. In the meantime, continued glassing of human colonies prompted HIGHCOM to greenlight RED FLAG, and as such, Cortana began sharpening her skills for her goal. Dr. Halsey other AI, Déjà also assisted them in their tasks.

Nearing the deadline, Dr. Halsey made a call for the SPARTAN-IIs to be brought to Reach, where they would be debriefed and ultimately embark on the riskiest human operation till date against the Covenant. She searched for a potential "carrier" for Cortana among the SPARTAN-IIs, eventually settling on SPARTAN-117, John, her favorite of the bunch and in her words the "luckiest". In order to test Cortana's likeness to her, she asked Cortana to pick her own carrier, and she too selected John, for being the most neurally compatible and having uncanny luck out of her candidates.

Fall of Reach

In August of 2552, Dr. Halsey began work on her investigation of the Babd Catha Forerunner Complex near SWORD Base as part of her study of the Covenant Hierarchy for RED FLAG. Since Déjà wasn't intelligent enough and Kalmiya's major fragment was elsewhere, Dr. Halsey thought Cortana would be the best choice of an AI to help her. Not wanting to interfere with Cortana's already tight schedule, Halsey "split" Cortana into two components. The major fragment was taken aboard the UNSC Pillar of Autumn as per her schedule, while the other fragment stayed with Halsey, neither of which could stay stable for a long time before reuniting. After Laszlo Sorvad, one of Halsey's fellow xenoarchaelogists was killed by a Sangheili Zealot during his investigation of the mysterious Forerunner complex, Halsey decided to go there with a bigger staff and more security, since Sorvad claimed that whatever he found could change the tide of the war before his death.

On the other hand, the major component of Cortana continued her work for RED FLAG. Soon after modifications were made to John-117's neural interface to be able to hold an AI's memory chip inside and be compatible with the MJOLNIR Mark V's features, he was introduced to Cortana. John was quickly surprised by Cortana's wit, her speedy skills and observations, and her clever humor. As part of a program to check the duo's effectiveness, John and Cortana had to undergo a test devised by Colonel James Ackerson, a long-time rival of Dr. Halsey and her SPARTAN-II Program.

While Dr. Halsey had suggested live-fire and a squad of Marines, Ackerson interfered and added more things to deliberately ensure John and Cortana would fail. He added a squad of ODSTs, a bunch of LOTUS Mines in a minefield, 30mm automated chain guns, and even a SkyHawk airstrike, complete with its 50mm cannons and Scorpion anti-tank missiles. Cortana nimbly helped John through the course by estimating positions of the mines, accessing Reach's satellites to inform him of the air strike, and inform him of the specific time instant at which he's slap and deflect a Scorpion missile aside, which would otherwise kill him. While she wasn't at her peak efficiency due to the fragmentation, Cortana did very well and was praised for her work. However, she was adamant about her negative opinion of Ackerson and hence took "revenge" by hacking into his personal records and blackmailing him, making it such that he'd be reassigned to the front lines instead of a safe corner somewhere.

Meanwhile, the other fragment had collected enough data from the Forerunner complex to be deemed extremely important and Dr. Halsey requested its transferral to the PoA. She chose NOBLE Team for the mission and its member SPARTAN-B312 as Cortana's carrier. However, events during Operation: UPPERCUT and its aftermath delayed the mission, and Cortana used this time to study more about the hidden complex. Soon later, NOBLE Team was given a new mission; destroy SWORD Base. However, they later learned that their 'real' mission was to safely deliver the Cortana fragment to the Autumn, which was currently docked at the Aszod Ship-breaking yards waiting. NOBLE Team successfully delivered Cortana's memory matrix to Captain Keyes, though at the cost of almost their entire team, including B312 who had volunteered to stay back on the planet and cover the Autumn as they escaped. She soon fell in battle, killed by various waves of Sangheili Zealots and other troops.

After the two fragments of Cortana were reunited, she was installed as the ship's primary AI instead of the ship's own AI, Wellsley, to test her maneuvering capabilities. She expertly piloted the cruiser in the battle against the seven hundred-ships invasion force on Reach from the Covenant. She easily destroyed a Covenant carrier while navigating through the asteroid belt, owing to her precision and also the lack of an onboard AI to make right adjustments on the Covenant ship. Under her control, the Autumn also intercepted and destroyed a new kind of Covenant warship that could "snipe" human ships from a distance.

However, all this would go in vain as Reach's defenses were broken through, their ODGs compromised, and the glassing of the planet's surface began. Captain Keyes ordered Cortana to take the Autumn through random slipspace jumps away from Reach as per the Cole Protocol, but a small but significant observation from John gave her an idea. The alien hieroglyphs and symbols found on both an artifact found on Sigma Octanus IV, and on the Babd Catha Complex during her research seemed to be stellar coordinates, and she used them in her random slipspace jumps, eventually leading them to Installation 04, the Alpha Halo.

Battle of Installation 04

Raid on Reach

Seemingly the last survivors to escape Alpha Halo before the Autumn's reactors destroyed the ring, Cortana continued to passively scan the debris field for any survivors at John's requests, despite disobeying his order to do an "active" scan that'd take weeks to process. The duo found floating cryopods that were ejected from the ship before crash-landing, but couldn't fire their engines to maneuver and retrieve them since that'd alert the nearby Covenant ships. She also detected an intact Pelican that was probably parked on an asteroid. Using atmospheric depressurization, Cortana accelerated the Longsword just enough for John to exit and grab the cryopods. This move alerted the Covenant ships and before John could reach the Longsword back and before the ships could fire, the Pelican suddenly jumped to life and shot missiles at the ships. Safely bringing the pods back, both the Pelican and Longsword escaped into the debris field, and after establishing contact entered a slingshot orbit around Basis having fooled the ships.

The duo, along with newfound friends Sergeant Avery Johnson, Warrant Officer Shiela Polaski, Corporal Locklear, and Lieutenant Elias Haverson quickly whipped a dangerous-but-rewarding plan; hijack the Covenant flagship later revealed to be the DDS-class heavy carrier Ascendant Justice and command it to escape the system. After busting through the hangar bay and barely surviving the overwhelming force, John inserted Cortana into one of the data ports present nearby. By then, Cortana was already looking forward to testing her capabilities, and she immediately took control of the ship's systems. She depressurized every part of the ship except the humans' path to the bridge so any attacking parties would die of asphyxiation, while in the meanwhile John and the others stormed the bridge and assumed control.

When deciding what to do next, John received an opposing vote from everyone save Johnson for his order of continuing Operation: RED FLAG using the hijacked ship. After a brief discussion, he relinquished his tactical command and set course for Reach, which Cortana immediately realized as trying to save his teammates. She complied and used the advantage of the Covenant ship's databanks to learn their lexicon more extensively, and also to create unstable personality spikes of herself that were able to perform as effectively as she could for a brief amount of time.


Battle of Earth

Battle of Installation 00

Stranded in Space

First Battle of Requiem

Death and Final Moments

Resurrection by the Domain

Although the major part of Cortana and her personality "died" after succumbing to her rampancy and was only barely able to create a hardlight shield to protect John from falling debris, her rampant personality spikes were intact, although a few were erratic. With the Mantle's Approach's structural integrity compromised, various segments of the ship detached and entered slipspace. They activated preset routines that would plot a course to any Forerunner installation, preferably a Shield world, as an automated response of fleeing the battle. One such segment, the "core seed"[2] of the ship reached Genesis, a Forerunner shield world housing a secret gateway to the Domain that was guarded by the Warden Eternal. However, this part of the ship also contained the various copies Cortana made to defeat the Didact, including the most stable one that still retained a bit of Cortana's personality but had a deteriorating lifespan.

Cortana found this gateway in the form of a tiny mote of light in the midst of the nothingness that she observed and perceived as her "death".

Characteristics and Traits

Physical Appearance

Cortana avatar.jpg
Cortana's avatar top-half.

Created to be one of the best "Smart" AIs of that time, Cortana's intellect and skills were crucial to the SPARTANs' survival in their infamous high-risk operation. For that, she had to be derived from the brain of the most intelligent person who knew the SPARTANs well and had knowledge regarding the Covenant. Believing the person to be none other than herself, Dr. Halsey convinced ONI to have her own brain carefully flash-cloned various times, much to their dismay. Only one of these brains would survive long enough for the brain to be scanned and replicated, giving birth to Cortana. Thus, as a result, Cortana was essentially Dr. Halsey herself, albeit a younger and more proud version of her.

Tapping into whatever few memories she had of Halsey, Cortana picked an avatar for herself. The result was a bluish tall, slender and semi-naked young girl in her 20s, with a striking resemblance to young Dr. Halsey. She had bits of code and symbols running through her skin constantly, with many darker blue lines partially covering her body. Dr. Halsey herself was impressed at her choice of avatar. At times, her avatar would change with minor variations, like the number of dark blue lines or turning from a bluish to a pinkish hue, but overall she looked the same.

Personality and Behaviour

Being derived from Dr. Halsey, Cortana possessed a personality largely similar to Dr. Halsey's younger self, with a few specific traits being exaggerated. As such, Cortana seemed to have an affinity for sarcastic humor and cheerfulness. She seemed to take a liking to be playful with her fellow UNSC soldiers, even on the battlefield. While a few people had initially felt discomfort with her quipping nature like John-117, others like Tyler-A319 were rather amused at how advanced an AI could become. Nevertheless, Cortana always knew when it was the time to make jokes and when it was not.

Having the most advanced infiltration capabilities and espionage skills coupled with Dr. Halsey’s wit and her characteristic traits made a deadly combination with Cortana. She was always proud to show off her abilities and leave her fellow comrades in awe of her actions. This directive of hers very rarely affected her mission, and Cortana always took care of that. However, as she slowly descended into rampancy, her control on it slowly started weakening too. This pride was probably the trait that resembled her creator the most during her young years. She also had a superiority complex that slowly began to fade as she grew older, that she was the best AI created and superior to everyone. This trait was reactivated once her rampant personality spike was reinvigorated by the Forerunner Domain and her directives/motives drastically changed.

She always continued to care for her teammates, always looking for ways such that they wouldn’t be in danger. However, this was only her Beta-level priority, as her Alpha-level priority was always to complete her mission, even if it meant sacrificing hers and her teammates’ lives. But Cortana always looked every alternative method to find out the best way possible. This was a concern to John, as he feared that one day she might consider the well-being of him and the other SPARTANs more than the mission, and his fear would finally come true when she turned rampant.

After she installed her rampant personality spikes into the ‘’Mantle’s Approach’’’s system, her personality began to deteriorate. She ejected her last non-corrupted duplicate to have one final conversation with John, while the rest of the spikes were destroyed, all except one. This one splice of hers was on the part of the ship that entered slipspace and exited at Genesis, where contact with the Domain gave her life again and amplified her minute negative thoughts on humanity caused by her superiority complex, which was amplified as well. The result was a new Cortana, who felt that humanity was dangerous to be left alone and must be put in check. She thus began her new mission; order and discipline all over the galaxy and all species submitting to the Created, and their queen being herself.

Skills and Abilities



"They let me pick. Did I ever tell you that? Choose whichever Spartan I wanted. You know me. I did my research. Watched as you became the soldier we needed you to be. Like the others, you were strong and swift and brave. A natural leader. But you had something they didn't. Something no one saw, but me. Can you guess...? Luck."
―Cortana, regarding her pairing with John-117.

"Sod off."
―Cortana, showing her annoyance.

"I can give you over forty thousand reasons why that sun isn't real. I know it because the emitter's Rayleigh effect is disproportionate to its suggested size. I know it because its stellar cycle is more symmetrical than that of an actual star. But for all that, I'll never actually know if it looks real... if it feels real. Before this is all over, promise me you'll figure out which one of us is the machine."
―Cortana, noticing Requiem's artificial star.


Fanon Appearances

Creator's Notes and References

  1. In Dr. Halsey's Journal—canonically dated May 21, 2549—it is mentioned that Cortana is a third-generation AI. This is highly unlikely, seeing as fifth-generation AIs were the standard for various years and were the most advanced then. As with Halopedia's theory, in this article, it is speculated that it merely means that upgrades were done for Cortana that gave her desired traits of third-generation AIs and not that Cortana was herself a third-generation AI, and would seem like something Dr. Halsey would personally do for RED FLAG.
  2. As mentioned on Halopedia.
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