The Weapon

"The Weapon" is the moniker of an artificial intelligence. She has the serial number of CTN 0453-0. She was created as an exact copy of the AI Cortana, designed to enter an installation to imitate Cortana and lock her down for retrieval.

Creation and Terminating Cortana
In October 2559, Dr. Catherine Halsey dispatches Blue Team on Operation: WOLFE to retrieve three cryobins and a lockbox from a cryovault beneath the ruins of CASTLE Base. Halsey insists that what they are retrieving is the key to stopping Cortana, although she warned John-117 that while it would not be easy, it is the only option that they have. The contents of the bins, the remaining cloned brains from Halsey's creation of Cortana, are used by her to create the Weapon for the mission of entering an installation to imitate Cortana and lock her down for retrieval. Halsey creates the Weapon to be an exact copy of Cortana with any information that could compromise the Weapon removed by Halsey. After her completion, Dr. Halsey introduced the Weapon to the Master Chief, and he was briefed on the plan to capture Cortana and deliver her to the for termination. Upon the Weapon's successful deployment, her deletion routine would be executed.

Zeta Halo conflict
Shortly after the Infinity arrived at Installation 07, it was ambushed by a Banished force led personally by Atriox. As the ship quickly became overrun, Captain Thomas Lasky ordered for the Weapon to be deployed immediately. Meanwhile, the Master Chief stayed behind on the Infinity to hold off the Banished as Lasky was escorted to a dropship. Once on the Halo, the Weapon was able to lock down Cortana in the Silent Auditorium. Cortana was destroyed, though not through means apparent to the Weapon. In reality, Cortana had willingly destroyed herself and damaged the ring in order to prevent Atriox from using it against humanity. She also deactivated the Weapon's deletion routine so that she could accompany John-117 during the struggles that lay ahead. And so, the Weapon was left active within the Foundation, believing that the Master Chief was due to come back for her.

Six months after the defeat of Cortana, the Master Chief is revived and returned for the Weapon, whom he is surprised to see is still functioning. Not knowing how or why her deletion was averted, she is recovered and accompanies him across Zeta Halo, which is now controlled by the Banished following the crippling of the Infinity. Recovering the framework that the Weapon had used to lock down Cortana, the two witness echoes of Cortana's life scattered across Zeta Halo's systems.

The Weapon helps the Master Chief as he travels across Halo, destroying a mining drill after he takes out the cooling pipes,, disabling one of the Spires and collecting data on the Reformation, and helping him to destroy three Banished AA guns.

However, in order to help the Master Chief access the Command Spire, the Weapon is forced to interface with four Forerunner beacons in order to override a lockdown on the Command Spire. Throughout her hacking, the Weapon is observed by another presence and it's only on the fourth beacon that she realizes that it's actually the Harbinger. The Weapon realizes that it's a trap with the Harbinger trying to break the deadlock on starting the Spires by combining the Weapon's routines with the Monitor's. The Master Chief suggests stopping and creating a stalemate, but the Weapon warns him that the Harbinger is close and that she will eventually find a way. With no other choice, the Master Chief allows the Weapon to proceed, but he discreetly activates a deletion protocol for the AI just in case. When nothing happens to her, the Weapon suggests that she was just being paranoid and the Master Chief dodges her question about what he was saying while activating her deletion protocol.

Later, while interfacing with Halo in the Nexus, the Weapon is trapped in the system by the Harbinger. The Weapon begs the Master Chief for help, but, worrying that the AI had been compromised, he went through the authentication to manually delete the Weapon instead. However, the Weapon manages to break free of the Harbinger's clutches and override the deletion protocol. The Weapon is livid that the Master Chief was willing to turn on her so quickly rather than trust in her to break free herself while he is furious that she stopped him and put them all at risk. The Weapon confirms that the Reformation has begun, but reveals that she has managed to steal data from the Harbinger using her infiltration abilities. The Master Chief continues to argue that she broke protocol, causing the Weapon to demand what is wrong with him as she was only trying to help them and it was worth the risk before activating a gravity lift.

The Weapon continues to accompany the Master Chief, but her tone now shifts to outright dejection and sarcasm towards the Chief, even telling the pilot what the Master Chief had done to her. The Master Chief and the Weapon make their way to the top of the Command Spire, defeating Adjutant Resolution once again. Once three attacking Banished Phantoms have been destroyed, the Weapon interfaces with the Command Spire, continuing to treat the Master Chief with sarcasm and dismay over his earlier actions. The Weapon, lacking her usual enthusiasm, shuts down the Spire network and successfully stops the Reformation before demanding answers from him, pointing out that she had waited for him for six months, done everything that he's asked and while she was supposed to be deleted, he's the reason that she's still here and he could never have accomplished all that he's done on Halo without her. The Weapon demands to know why he can't trust her like she had trusted him, and he brings up Cortana, but the Weapon tells the Master Chief that Cortana is dead and all that's left of her are echoes that will be gone too sooner or later. Echo 216 arrives with the news that all of the Spires are shutting down and the Weapon informs the two men that while the Master Chief is ready for pickup, she's staying in the Command Spire. The argument is interrupted by Jega 'Rdomnai attacking the pilot in the cockpit and flying off with him after the Master Chief can't get into the Pelican to rescue him. The Weapon warns the Master Chief that the pilot doesn't stand a chance against a Spartan Killer, and he orders the Weapon to track them and open a portal to somewhere close by. The Weapon argues against this, warning that they could die trying as it's hard to lock down the coordinates, but he has her do it anyways and they depart through a portal in pursuit of 'Rdomnai and the pilot.

The echoes across Zeta Halo eventually lead the Weapon to discover her true nature as a copy of Cortana, and she then decided to allow the Chief to go through with her deletion for fear of going power mad herself. However, the Spartan refuses - admitting that while he doesn't trust the AI completely, he wants to.

The Weapon eventually deduces that her deletion had been prevented by Cortana herself, after reviewing echoes Cortana had deliberately left in the Silent Auditorium for them as a form of archive. They recorded Cortana's inner thoughts and her exchange with the Banished leader Atriox following his attack on the Infinity, all of which amounted to her realizing that she unwittingly set in motion a chain of events, which would put all life in the Milky Way in mortal danger. Cortana knew that the Weapon would be John's sole option for stopping the plans of the Banished, as she would no longer be able to.

After the defeat of the Harbinger, the two witness a final message recorded for the Master Chief by Cortana, in which she apologized for her actions and hoped that the two may learn from her mistakes and become better for them. Cortana also relayed to the Master Chief that she felt that the Weapon had a lot of potential. After reuniting with the pilot, the two learn his real name and the Master Chief offers to let the Weapon choose her own name - much like Halsey had done for Cortana. The Weapon informs her companions that she had the perfect name for herself.

Personality and traits
The Weapon has a sunny and naive personality due to her young age and lack of experience. Due to Halsey apparently limiting the information that the Weapon has access to, she lacks basic knowledge on things such as what the Banished and even the ex-Covenant species such as the Hunters are. However, she shares some traits with Cortana such as often snapping her fingers when performing an action and, due to possessing the same routines and systems as Cortana, she possesses Cortana's skill in hacking into alien systems and retrieving or sabotaging things. The Weapon sometimes does this with enough of a dramatic pause before finishing that that the Master Chief asks her if something's wrong before the Weapon snaps her fingers and completes what she was doing. However, after the Master Chief tries to delete her, the Weapon is deeply upset as he was supposed to protect her and they were supposed to be a team. As a result, she takes on a more dejected and sarcastic tone while dealing with him. While shutting down the Spire network, the Weapon loses all of the exuberance that she had previously showed, simply stating that it had worked and that no there was not a problem before simply counting down and snapping her fingers, the exact opposite of when she would purposefully put in a dramatic pause before completing one of her tasks.

After discovering her true origin, the Weapon is horrified because of the terrible things that Cortana, who is essentially her, has done and she tries to delete herself. However, the Chief stops her, stating that while he does not trust her, he wants to, recognizing the differences between Cortana and her copy. Cortana herself notes that the Weapon has a lot of potential and that she makes a great replacement as the Master Chief's AI companion.

Trivia

 * The Master Chief's deletion code for the Weapon is "RED FLAG 034 SAMUEL." Operation: RED FLAG is the mission to the Covenant homeworld High Charity that the Master Chief and Cortana were supposed to embark upon when they first met while Samuel-034 was his best friend before Sam died in the Battle of Chi Ceti in 2525.
 * In Halo Infinite, the Weapon first transfers into the data crystal chip by touching it in the same way that Cortana did in Halo 3 before transferring into other systems by the Master Chief touching them like Cortana did in Halo 2, albeit with the Master Chief first manifesting a hologram of her above his hand.
 * In Halo 4, Cortana briefly predicts the future partnership of the Master Chief and the Weapon at the end of the level Composer, telling the Master Chief that "they'll pair you with another AI. Maybe even another Cortana model if Halsey lets them. It won't be me, you know that, right?" In her final message to the Master Chief, Cortana jokingly echoes this statement to him.

List of appearances

 * Halo Infinite