The All-Mother
Mostly limited to the Nora, the All-Mother is an earth goddess who is, or resides in, All-Mother Mountain. She is the source of all life — humans, machines, or otherwise. The area near All-Mother Mountain is known as the Embrace, which has the second figurative meaning of the All-Mother looking favorably upon you.
The apocalypse which wiped out the Old Ones came about because they began to put their faith in the machines instead of the All-Mother. The Metal Devil, the most powerful among the machines and personified by the war machine still dormant atop the mountain, turned on the Old Ones and slaughtered the faithless ones. Only the faithful were brought into All-Mother’s Embrace, into her mountain, and protected long enough for her to strike down the Metal Devil, leaving the corpse frozen where it still stands.
In addition to the All-Mother, Nora have extended this belief to also put importance on strong matrilineal relationships. Mothers are the head of the family, thus disrespecting or being without a mother are great offenses.
As the Nora do not record a written history, there are no records of the evolution of this belief. However, holo-recordings of events inside ELEUTHIA-9 reveal that, of the multiservitors which raised the first generation of humans, the “mother” persona was considered more favorably due to her more comforting demeanor. Once the humans were locked out of the mountain, this likely became a desire to be re-accepted by the mother-figure in the mountain, leading to the modern belief in the All-Mother.
While GAIA does have non-interference directives regarding the humans of the outside world, it is not clear whether any interactions with the Nora occurred before the return of Aloy. Such interactions, whether in holographic form or as a disembodied voice, would only reinforce the belief in an All-Mother inside the mountain.