Gróa

Gróa was a Jötunn seeress and one of the most powerful practitioners of seidr in the Nine Realms. The wife of the warrior Aurvandil, she devoted herself to gathering arcane knowledge in the hope of finding her lost husband, and in doing so became the first being ever to foresee Ragnarok. Her gift drew the attention of Odin, who murdered her to hoard her vision, never realizing that what she had given him was a lie. Long after, Kratos and Atreus found the shrine where her story was kept. (God of War (2018); The Lost Pages of Norse Myth; God of War Ragnarök)

The seeress of Jötunheim#

Gróa was a Jötunn of great power, a sorceress and practitioner of seidr born of the line of the giants. At some point she married Aurvandil, and when Thor asked the warrior to aid him on a quest, Aurvandil went with the thunder god and was lost in the tundra, never to return. Grieving and determined to learn his fate, Gróa traversed the realms in search of ancient tomes that might augment her prophetic powers. (The Lost Pages of Norse Myth; God of War (2018))

In the course of her searching she became one of the most gifted practitioners of seidr the realms had ever known, so accomplished that even Odin would come to her seeking knowledge. Yet for all her power she could learn nothing of her husband's whereabouts. (The Lost Pages of Norse Myth; God of War (2018))

The prophecy of Ragnarok#

After reading a set of runic incantations in an ancient tome, Gróa's powers swelled to such heights that she beheld a vision of the end of the world. She saw a three-year winter in which the realms quaked and the skies split, a terrible figure emerging with a flaming sword, an enormous wolf, the gods turned against one another, and a white ghost from another land standing with his son at the center of the events that led to it all. She was the first being ever to foresee Ragnarok. (The Lost Pages of Norse Myth)

Odin sensed that she had glimpsed the future and came to her library demanding to know what she had seen. She knew him as a longtime patron of her services and welcomed him as a friend. He pressed her, and at last confessed that it had been Thor who killed Aurvandil. Refusing to give him the prophecy, Gróa was seized by the throat and strangled to death by a smiling Odin, at least in the version Mimir tells,, who took her library and her knowledge for himself. (The Lost Pages of Norse Myth; God of War (2018))

The hidden truth#

What Odin believed he had taken from Gróa was not the truth. A secret found in her shrine later reveals that the prophecy she gave him was a deception, told so that the real vision of Ragnarok would stay hidden. That account also has Odin killing her with his spear rather than his hands. The shrine itself, a Jötnar triptych showing her tome chest, her vision of the end and Odin's betrayal, stands in a temple in Alfheim, where Kratos and Atreus come across it long after her death. In Mimir's telling she saw further than anyone before her or since. (God of War Ragnarök; God of War (2018))