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 insisted that what they are retrieving is the key to stopping Cortana, although she warned John-117 that while it wouldn't be easy, it was the only option that they had. The contents of the bins, the remaining cloned brains from Halsey's creation of Cortana, were used by her to create the Weapon for the mission of entering an installation to imitate Cortana and lock her down for retrieval. Halsey created the Weapon to be an exact copy of Cortana with any information that could compromise the Weapon removed by Halsey. According to the Master Chief, the weapon was "basically Cortana if the two of them had never met".

After her completion, she was partnered with the Master Chief, so he could take Cortana to the for termination. Upon the Weapon's successful deployment, her deletion routine would have executed. However, while she succeeded in locking Cortana down, the routine failed to activate, causing her mission parameters to change to ascertain why she was not terminated.

Zeta Halo conflict
The Chief successfully deployed the weapon on Zeta Halo and, assuming the Weapon has deleted itself according to plan, returned to the UNSC Infinity. However, the Weapon's deletion did not go through as planned, and she was left active in the Foundation on Zeta Halo, believing the Chief was due to come back for her.

Six months after the defeat of Cortana, the Master Chief was revived and returned for the Weapon, whom he was surprised to see still functioning. Not knowing how or why her deletion was averted, she was recovered by him and went on to accompany him across Zea Halo - the installation 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 witnessed echoes of Cortana's life scattered across Zeta Halo's systems. While interfacing with Zeta Halo at the Command Spire, she was momentarily trapped in the system by The Harbinger, who had been monitoring her to learn how to work the ring's systems. Master Chief, worrying the AI had been compromised, went through the authentication to manually delete the Weapon only to be overridden by the AI. The Weapon was livid that Master Chief was willing to turn on her so quickly, rather than trust in her to break free herself. She would continue to work with him, though her tone now shifted to outright dejection and sarcasm towards the Chief. The echoes across Zeta Halo would eventually lead the Weapon to discover her true nature as a copy of Cortana, who then decided to allow the chief to go through with her deletion for fear of going power mad herself. However, the Spartan refused - admitting that while he doesn't trust the AI completely, he wanted to.

The Weapon eventually deduced 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 which amounted to her realizing she unwittingly set in motion a chain of events, which would put all life in the Milky Way in mortal danger. Cortana knew 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 witnessed 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 the Weapon had a lot of potential. After reuniting with the Pilot, the two learnt his real name and the Master Chief offered to let the Weapon choose her own name - much like Halsey had done for Cortana. The Weapon informed 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.

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 doesn't 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