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In the Halo franchise’s early days, Doctor Catherine Halsey was perhaps the most important secondary character in the entire series. She’s the mastermind behind the Spartan-II project, a military program that kidnapped children and turned them into the covert super-soldiers she believed could stop humanity’s slide into conflict and chaos. And when humanity suddenly found itself at war with the Covenant, Halsey used her know-how to aid and equip humanity, deciphering the secrets of scavenged alien tech to give the United Nations Space Command and humanity an edge. The Spartans proved to be the most effective weapon in humanity’s entire arsenal.

But as Halo‘s universe has widened and the story of the games has continued, it’s hard to say what role Halsey plays any more. In Halo: First Strike and Ghosts of Onyx, Halsey breaks with the UNSC, seeking to atone for her past misdeeds by rallying as many Spartans as she can and hiding them from what she believes is a lost war and the possible end of the galaxy. As it turns out, humanity triumphs against the Covenant and the Flood, and upon reconnecting with the UNSC, Halsey is promptly arrested for her actions.

In Halo media, Halsey has played a number of roles—macguffin to be recaptured in “The Package”, a way to backfill a reason for why Noble Team was important to the universe in Halo: Reach, and general explainer-of-technical things in Halo 4‘s Spartan Ops. The end of the latter sees Halsey in the clutches of Jul ‘Mdama’s Covenant and rather peeved that the UNSC tried to execute her, but circumstance end up sending her back to the UNSC’s side by the events of Halo 5.

But what role does Halsey play beyond that? It seems like her quick return to the fold and the tabling of old grudges in Halo 5 is mostly to bring her back to the role of “explainer of things, crafter of scientific plans”, and while that’s a legitimate character role, there’s no reason that can’t be fulfilled by Glassman (if he could stop getting captured), or any of the other scientists we’ve seen in Halo since.

Herein lies the problem with Halsey—she doesn’t have any obvious room to grow as a character. Not every supporting character in a story needs an arc, but Halsey’s personal journey has essentially moved her past relevance to the story and themes Halo is currently telling. The Reclaimer Saga is shaping up to be about inheriting the Forerunner’s legacy and the Mantle of Responsibility, but Halsey doesn’t have much of a personal connection to this. She nearly claimed the Absolute Record in the Escalations comic series, but ended up losing that chance. So where can she go from here?

The Kilo-5 trilogy and a lot of the post-Halo 3 universe has shone a light on Halsey’s monstrous actions and her being fine with climbing on top of skulls in the pursuit of scientific knowledge. Halsey may not be a “bad person” deep down, but she’s done some pretty horrible things. Even if she had the willing help of a deeply suspect government helping her along the way, it doesn’t absolve her personal responsibility. Under normal circumstances a character with such a checkered past could have a redemption arc—a way to atone for past misdeeds. Media under 343 Industries has begged the question by making Halsey’s actions a focal point of the wider universe and how it relates to the more “personal” approach to the Master Chief. But the problem has always been, how can Halsey be redeemed? Through the efforts of the Spartans and Master Chief, her work indirectly saved humanity (just not from the threat she originally envisioned). What could she possibly do that would matter more than that? And what sort of trial would speak to Halsey’s personal demons and her own desires? Until Halo 5, there was really nothing in the universe that could fit the bill for a Halsey redemption arc, and then…

It’s a pretty common trope in fiction that the villains are twisted mirror versions of the heroes, but when you break it down Cortana actually fits that role to a tee vis-à-vis Halsey. Cortana was both Halsey’s prime technical achievement and perhaps her biggest ethical failing—breaking the Mortal Dictata, she covertly created clones of herself to harvest their brains to create a next-generation AI. The descriptions and sketches in Halsey’s Journal of her misshapen “sisters” before she terminated them is pretty horrifying. But the morally dubious process gave birth to Cortana, essentially more of Halsey’s daughter than Halsey’s daughter was (sorry, Miranda) and a true breakthrough in A.I.s.

But what is Cortana’s plan for her and the Created, but taking Halsey’s desire for stability and order to a pretty crazy extreme? For Cortana, the greater good means the ends justify the means—and thus far the ends have been thousands of lives lost to the Guardians she deployed to keep the peace. Cortana’s shift from her personal focus on her mission and her Spartan to controlling the fate of the galaxy is just a giant-sized inversion of Halsey’s own heel realization arc, where she started out fueled by dispassionate utilitarianism but ultimately began focusing on something more personal. After being saved from the ruins of Reach in the events of the novel First Strike, Halsey goes AWOL precisely because she no longer believes in those utilitarian tenets the way she did in her youth. She tells Cortana, “I’m tired of sacrificing others for the ‘greater good’. It never stops, Cortana… and we’re running out of people to sacrifice.”

That dueling outlook is what drives many a great and storied conflict, but it has even greater resonance because of Cortana and Halsey’s differing views on where humanity goes from here. For Cortana, the intellect and immortality offered to A.I.s via the Domain means they are uniquely positioned to decide the fate of the galaxy—where Halsey and ONI and the greater UNSC failed to bring peace through subjugation, A.I.s operating on an immortal timescale and backed up by Forerunner tech can succeed. But Halsey champions the Spartans—whom she calls humanity’s destiny as a species. It’s a question of whether people are fit to govern themselves, however unwisely, and whether peace through subjugation is any sort of peace at all.

In Cortana, then, Halsey sees the ultimate manifestation of her earlier beliefs in the power of a single organization to unify and control people, taken to its logical and perverse extreme. This is the perfect battle for her to fight, because she has a deeply personal stake in it—essentially she is fighting her own ghosts and the poisonous ideals she has since discarded, reincarnated.

With the power of the Guardians at her disposal, the UNSC is on its back foot for the first time since they miraculously came out on top after the Human-Covenant War, and it’s here that Halsey can become more than just another scientist. Like it or not (and it’s clear a lot of the UNSC doesn’t) Halsey is still one of the foremost minds on A.I.s and Forerunner tech, which now are the most important topics in the galaxy. She becomes essentially the only person alive in the universe who stands a chance at helping mount a resistance, and her decisions going forward give her an agency her character has basically lacked since her capture in the Kilo-5 Trilogy—stopping Cortana isn’t something she’s going to be ordered to do, but something she has a personal stake in. Her entire vision of humanity is threatened, and history has shown that, just like her A.I. child, Halsey will fight for what she believes in. It’s a tantalizing set-up that brings together long-running plot threads in the Halo universe in a story arc that some fans have criticized for abandoning a lot of the post-Halo 3 threads 343 Industries established.

If 343 Industries jumps at the chance for Halsey to step out of her technobabble role in the games and show the universe what she’s made of, it took them long enough.