GAIA
The original AI from which the other Subordinate Functions split, GAIA was created by Elisabet Sobeck and the other Alphas of Project Zero Dawn to be the overseer of the regeneration of Earth’s biosphere and human population. Portrayed as an anthropomorphic hologram of a dark-skinned and middle-aged woman, GAIA had a demeanor befitting her earth-mother namesake. Defying the laws of the time, Dr. Sobeck imbued GAIA with emotion, empathy, and curiosity, which she saw as vital for any AI complex enough to take on such a human-oriented task.
While GAIA’s efforts were successful, evident from Earth’s functioning ecosystem and growing human contingent, outside influences ultimately brought the AI to an early end. In an attempt to contain HADES after it and the other Subordinate Functions had been released, GAIA set off a self-destruct at GAIA Prime, the underground facility which housed the AI’s compute resources. This destroyed GAIA, leaving only prerecorded holographic echoes to be discovered decades later by Aloy.
Non-Interference Directives
Project Zero Dawn left GAIA with constraints around how much the AI could interact and interfere with the human population. These directives were not stated explicitly in HZD, but were said to limit GAIA’s ability to reveal the truth of ELEUTHIA-9 to the Nora population.
From a narrative perspective, these directives are odd — if the Alphas believed APOLLO would work, and all humans would grow up knowing exactly what GAIA was, such limitations would be unnecessary. This could be interpreted as a plot hole, but Skyline chooses a more interesting interpretation: it wasn’t the Alphas who added them, it was Ted Faro. Ted was already convinced humanity would suffer if too much was carried over between the epochs, but he still needed GAIA to function long enough to restart the human race, and to do so hands-off. It would be reasonable to him to add non-interference constraints, and then to build out a contingency to dissolve GAIA once the humans had reached a state where they could continue on their own. Being Ted, it wouldn’t occur to him that he might get that part wrong, freeing HADES to undo all that had been done.
GAIA in Skyline
With the exception of the above conjecture about directives, Skyline sticks to the Horizon lore for GAIA.