The Weapon

"The Weapon" is the moniker of an artificial intelligence, she has the serial number of CTN 0453-0. She was created to enter an installation to imitate Cortana and lock her down for retrieval. The Weapon is actually an exact copy of Cortana herself, with all of the same routines and systems but with any information that could compromise her removed.

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 warns John-117 that while it won't 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 whose mission is to enter 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. According to the Master Chief, she is basically Cortana if the two of them had never met.

After her completion, she is partnered with the Master Chief, so he could take Cortana to the for termination, and, upon the Weapon's successful deployment, her deletion routine would execute. However, while she succeeds in locking Cortana down, the routine fails to activate, causing her mission parameters to change to ascertain why she was not terminated.

Zeta Halo conflict
Six months after the defeat of Cortana, the Master Chief returns for the Weapon who accompanies him across the ring. Recovering the framework that the Weapon had used to lock down Cortana, the two witness echoes of Cortana's life, causing the Weapon to eventually discover her true nature as a copy of Cortana. The Weapon tries to self-delete once again, but she is stopped by the Master Chief who admits that while he doesn't trust the AI completely, he wants to. The two learn from the echoes that Cortana had sacrificed herself to destroy part of the ring and that it was Cortana herself who had stopped the Weapon's deletion, knowing that her best friend would need the other AI.

After the defeat of the Harbinger, the two witness a final message recorded for the Master Chief by Cortana who apologizes for her actions and hopes that the two learn from her mistakes and become better for them. Cortana also tells the Master Chief that the Weapon has a lot of potential. After reuniting with Echo 216's 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 has 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