Juliana was a UNSC "smart" AI operating on the Rubble. She was an Insurrectionist AI, who was originally a commercial AI used by miners from the colony of Madrigal. When she met the Gray Team, she was going through stages of Rampancy, yet didn't seem to be showing it. As she said, she hung onto the edge of Rampancy, trying to go back.
The humans of the Rubble coexisted with a group of seemingly peaceful Kig-Yar who were secretly trying to find the navigation data that would provide them Earth's coordinates. In order to prevent this, Juliana helped members of Gray Team recover the navigation data, rescue Lieutenant Keyes and the ODST's, and evacuate the citizens of the Rubble to the Exodus Project. Juliana who had already been rampant for some time, offered to drive the remains of the Rubble down onto the surface of Metisette.
Despite having been rampant for some time, Juliana did not engage in aggressive or destructive behavior like some AIs. The reason for this being that, like she said, the Rubble meant so much to her that the necessity of keeping it running and thriving held her sanity together. Juliana was also willing to die rather than leave the Rubble when offered the choice of boarding the Midsummer Night by Lieutenant Keyes, instead choosing to go down with the Rubble. Certain elements of her behavior strongly pointed to rampancy, however, such as a somewhat egotistical sense of her own greatness. This was not exaggerated, but her manner of thinking of herself as almost a god was unusual. The strong liking that she took to Jai, the Spartan leader of Gray Team, was somewhat strange. Little is known of her personality before she went rampant.
- Her character's role is surprisingly similar to Sif's from the previous book, Contact Harvest. Both are A.I.s that are or eventually end up rampant and sacrifice themselves aboard space stations, the Tiara for Sif, and the Rubble for Juliana, ultimately for the better of the UNSC forces nearby.
- Juliana held the safety of the Rubble higher than any personal interest of the leading council. Despite the council's ruling that they be given the navigation data, she helped Gray Team to retrieve the data and rescue the ODST's from confinement, also against the ruling of the council.
- Despite being a commercial AI and not having code-breaking skills, Juilana displayed skills at points comparable to those of Cortana, most notably her ability to hack Covenant systems and mine them for data once plugged in. Cortana was able to do that due to her advanced programing. Notably however, she lacked the ability to listen into and hack into the Covenant Battlenet without a direct connection, which Cortana could do.
- Her name contains seven letters, a potential 7 reference.
- Halo: The Cole Protocol (First appearance)