From Halopedia, the Halo wiki
Déjà was a "dumb" artificial intelligence who assisted Dr. Catherine Halsey with the SPARTAN-II Program. She took on the form of an ancient Greek goddess wearing robes. Déjà's intelligence within her fields of expertise was equivalent to a human IQ of 240.
Déjà served as an educational AI; a "teacher" for the SPARTAN-II training program. She instructed the SPARTAN-II supersoldiers in their first stages of training at Reach Naval Academy and other facilities on Reach. Her counterpart, Chief Petty Officer Franklin Mendez, gave the Spartans rigorous physical training. This, along with Doctor Catherine Halsey's physical augmentations and eventually MJOLNIR armor, made the Spartans more intelligent, stronger, and faster than their non-augmented counterparts.
Déjà's lessons were the part of the Spartans' training program meant to teach them to employ strategic thinking. She also educated them in history, mathematics, and presumably other fields. In one of her first lessons, she taught the Spartan-IIs about the famous Battle of Thermopylae, where 300 Spartans made a stand against a quarter of a million Persians. Another lesson was about seven wolves taking down a moose, by working as a team. This served as one of the Spartans' earliest lessons about the importance of teamwork; that a wolf alone would be a far less effective hunter than if it were accompanied by its pack. During one of Mendez's training missions, she helped the Spartan trainees when John-117 called her instead of Mendez. Using a mail link, he linked her to an Albatross dropship to request she show him how to fly it to get the Spartans home. While she couldn't do that, she had him activate the autopilot, allowing her to take control of the craft and fly the Spartans home herself remotely.
Déjà also acted as a sounding board for Dr. Halsey, discussing how the Spartan-II Program should be run. For example, the night the program officially began she advised Halsey on how to address the children. They also would discuss the treatment of the individual Spartans, as well as the ethics of their situation. As a "Dumb" AI, Déjà would tend to take the less emotional, more clinical side of these discussions: One example is when she asked Doctor Halsey if she was giving Soren-066 the choice to proceed in the program in order to alleviate her own conscience.
On March 31, 2526, Doctor Halsey sought Déjà's help in figuring out where a Covenant supply depot was based off the recovered Covenant kelguid and the arrival of the second logistics fleet to Etalan five days after the destruction of the first one. Déjà suggested that Covenant had instantaneous interstellar communication, allowing for the location they were looking for to be a planet five days slipspace travel from Etalan of which there was one. During this time, Déjà glitched, experiencing several erratic pauses. By this point, Doctor Halsey had traced the source to a sophisticated data miner slipped into her lab's systems by Hector Nyeto or one of his operatives. She didn't bother to correct it because Nyeto had already gotten access to her most closely guarded data and Doctor Halsey didn't want Nyeto to know that she was onto him. Doctor Halsey realized that Déjà's explanation was the most likely answer for the problem. Déjà then took her leave as Colonel Marmon Crowther arrived to talk with Doctor Halsey.
Her current fate is unknown. As a "dumb" AI, her lifespan is, in theory, indefinite. Déjà was seen on Reach in 2552, residing inside CASTLE Base. She was most likely destroyed when CASTLE Base collapsed.
Her name means "already" in French.
List of appearances