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When you think of characters in the Halo series, your mind immediately goes to Master Chief, Cortana, The Arbiter, and all the weird and wonderful aliens the franchise has conjured up over the years. Some are more memorable than others, but perhaps the one that’s been given the most emotional range and story arc (with Chief coming as a close second) would be Cortana.
This holographic AI is a stalwart companion and emotional rock throughout. Though there are moments of comic relief, Cortana is ironically the most human of the recurring cast and without her, Halo just wouldn’t be the same. Her appearances haven’t always been as just a voice in Chief's head because she’s managed a lot of running around in the vast reaches of space, her most recent of which involved trying to kickstart a move for ruling the entire galaxy. With her appearance in Halo Infinite seeing her at the head of an army of Guardians and Forerunner fleets dominating the galaxy, here’s what happened to Cortana and the rocky road that led her to where she is now.
Who Is Cortana?
Before diving too deep into things, there are undoubtedly going to be those who have no idea who this character is. To permit an introduction, Cortana is an Artificial Intelligence that is self-aware and based on the brain scans of Dr. Catherine Halsey.
Her first appearance in the series was in Halo: Combat Evolved as a helpful AI companion, but as the franchise trundled on she would take on a more central role with her current position being the major antagonist of the series. She's come a long way from being just a support character and her journey to get there is just as memorable and equally fascinating.
Cortana's Origins
Cortana's origins are unsurprisingly monstrous, considering Dr. Halsey's involvement. Essentially the good Doctor cloned herself using the same method by which she made the duplicate children for the Spartan-II Programme. These unfortunate creations were different however in that their brains were genetically altered to have higher mental agility at the cost of their physical abilities, making them smarter whilst also, unfortunately, deforming the vast majority of them.
After further experimentation, Halsey was able to graft the consciousness of a small handful of the clones onto an AI matrix, with the resulting intelligence calling itself Cortana.
In her early days, Cortana would regularly play chess with Dr. Halsey and as her charge learned and grew, the good Doctor was surprised by her unnaturally fast progress. Most notably when Cortana managed to deactivate termination codes Halsey had placed on her.
According to game lore (rather than that from the books), Cortana would later be brought to the attention of ONI and whilst scanning navigation data onboard an alien ship found buried in an ice shelf on Reach, she would be handed over to the crew of the UNSC Pillar Of Autumn. From there Cortana would go on to meet John-117 after navigating the Pillar Of Autumn to a distant Ring installation, and we all know what happens next.
Cortana's Appearances In The Halo Series
There’s no disputing that Cortana is a staple character of the Halo series, and she’s undoubtedly a fan favorite. With numerous appearances both within the Halo video games and outside of it in various pieces of the canon via books and graphic novels. It can be a little tricky, especially for newer fans, to piece together her arc and figure out how she ended up where she did once the dust settled, so with that in mind, here’s a brief rundown of Cortana's role within the main Halo story.
Cortana In Halo: Combat Evolved
Fresh off an extremely brief appearance in Halo: Reach (the prequel to Halo: CE) Cortana’s role was one of support to a fresh-faced Master Chief and a newly discovered alien enemy, The Covenant. Helping him through the mystery behind the Rings and the parasitic Flood hidden within its foreboding technologically advanced depths. After helping Chief discover the true purpose of the Rings, the two would go on to detonate the Pillar Of Autumn's reactors, with the entire Forerunner station being torn apart as the two along with four other surviving UNSC crew members escaped.
Cortana In Halo 2
Cortana successfully aids Chief and the four UNSC crew members take over a Covenant warship and intercede in a planned invasion of Earth. Master Chief and Cortana then end up on Delta Halo, where they interfere with the Covenant's plans to fire the ring and get embroiled in another confrontation with the Flood. She is left behind on the Covenant city of High Charity in case she needed to destroy the ring by blowing up the city. However, she is stranded when Chief returns to Earth, left with nothing but a Flood Gravemind for company.
Cortana In Halo 3
Cortana is mostly absent from Halo 3 until about midway through the game, though she does appear to Master Chief in a series of cryptic visions and clues scattered throughout key points in the story. She would later be recovered still onboard High Charity. Cortana and Master Chief were still able to destroy the last remaining Flood menace in the galaxy, detonating a gigantic Halo installation known as The Ark by prematurely firing Halo Ring Installation 08 at it within close range.
Cortana In Halo 4
After spending four years adrift in space alone whilst Chief slumbered away in Cryostasis after the gigantic explosion of The Ark sent the two hurtling through Slipspace, Cortana once again reawakened Master Chief as the two orbited around a Forerunner Shield World. At this point in her life cycle, she was nearing the end and suffering from pronounced Rampancy.
Upon reaching the surface they attempted to contact the UNSC using Forerunner tech, though in their attempts to call for help they accidentally released The Didact, a genocidal Forerunner that was sealed away thousands of years prior. Through a brutal battle, the two were able to defeat The Didact, although Cortana was seemingly destroyed in the process.
Cortana In Halo 5
As it turns out Cortana survived destruction as she had been uploaded to The Domain, a big hard drive used for storing the imprints of Forerunner consciousness. This process seemingly cured her of her Rampancy but left her matrix splintered into fragments, dispersing her consciousness throughout the network.
After recollecting herself and encountering an ancient Forerunner AI known as the Warden Eternal, Cortana's dark plans for the universe took form. She would take control of the galaxy using a vast Forerunner army, gigantic Guardian robots, rallying like-minded AI constructs to her cause, and spreading her warped vision of unity throughout the galaxy with an iron fist. Conflicted, Master Chief tried to convince Cortana to come back home, but he failed.
Cortana Pre-Halo Infinite
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Cortana is now the grand ruler of a dark mechanical imperium, after taking over most of the Sol system with her AI buddies, killing thousands either intentionally or not. One particularly disastrous encounter involved firing an energy pulse aimed at UNSC Infinity, which missed and knocked out power to half of the planet Earth resulting in a lot of accidental deaths.
What followed after the events of Halo 5 was a brutal campaign from a once gentle character and her cadre of Rampancy-cured AI as they took over worlds, reclaimed Forerunner technology, and announced themselves the true guardians of the Mantle Of Responsibility. Their following reign was like a dark shadow of The Forerunners as they terraformed planets, sometimes re-arranging continents for more optimum terraforming results with the current inhabitants perishing as a result.
Before Halo Infinite, Cortana enacted a surprisingly cruel and emotionless will over all organic lifeforms in the galaxy with a warped sense of doing things “for the greater good”.
Spoiler Warning Ahead
Cortana In Halo Infinite
During this period Atriox, the leader of The Banished and a large army of his boys manages to confront Cortana on Zeta Halo at the same time Master Chief appears with the UNSC and an AI known as The Weapon with the plan of containing Cortana and deleting her. The resulting conflict leaves a brutal and bloody aftermath in the stars above the ring. During this huge battle, the UNSC is defeated, and after being contained on Zeta Halo by The Weapon and cornered by Atriox, Cortana has a confrontation with The Banished leader where she asks him if he knew the future would he change anything. After replying no, Cortana seems to come to a realization about the error of her ways. She detonates a chunk of the Ring, preventing The Banished from using it as a weapon and killing both herself and Atriox.
Six months then pass and after waking up from stasis inside his suit onboard a Pelican, and after hearing that Cortana was deleted after all during her confrontation with Atriox, Master Chief heads to Zeta Halo to stop the remaining Banished forces led by Atriox's second-in-command, Escharum, and The Harbinger from unleashing The Endless, an ancient alien race imprisoned by The Forerunners. During this time echoes and memories of Cortana appear to Chief and The Weapon, with them becoming more direct over time as she expresses regret for her actions as they begin to appear to be more like messages left behind by Cortana. The culmination of all these recordings is a heart-breaking last recording to Chief that Cortana made before she was destroyed.
Cortana remarks that the two need to learn from her mistakes, become stronger, and that she "chose well" in Chief. The old friends share one last scene together before the recording of Cortana walks through Chief, disappearing forever. Her former friend and partner is left standing there speechless as the facility starts to collapse around them, before Chief and The Weapon escape through a teleporter. They're then rescued by Echo-216 and later return to Instillation 07 to finish the fight against the remaining Banished forces.
It's an emotional and gut-wrenching moment for fans of the series and after going through such a long journey, Cortana's Arc rounds itself off with a nice tight bow, The Weapon taking on her mantle and bringing a new, younger generation into the Halo series.
Cortana’s Rampancy
Though being a UNSC AI may come with a lot of perks, they do unfortunately have quite a short shelf life, with most lasting a maximum span of seven years before they need to be deleted. This is because as time goes on, all AI falls to an effect known as Rampancy. A process whereby an AI essentially overthink itself to the point of becoming a dangerous threat.
When AI's are created they were based on scans of brain tissue, this residual tissue allows for their ability to learn as well as process things emotionally, but these emotions are what can lead them to eventually become rampant. Basically, they can retain an infinite amount of knowledge, but can only emotionally process so much of it before becoming overwhelmed.
At which point they suffer from anger, anxiety, depression, and in the final stages they go completely off the deep end, losing all connection to reason and sense of self.
It's an unforgiving affliction that all AI are doomed to fall to as Human technology is not advanced enough to repair or save them. That was until Cortana unintentionally discovered a cure to her Rampancy when she was uploaded to the Forerunner Domain, something that she would use to lure other Artificial Intelligence-based beings to her side.
With her role in the series winding down, this is the last time we will see everyone's favorite digital lady in blue. But her Spartan charge seems to be in good hands going forward in their next fight against the mysterious Endless.