Ragnarok was a word deeply etched in the minds of the Asgardians. The origin of the prophecy itself was a mystery and all the Asgardians knew about it came from the giantess Grea, the only giantess allowed to remain among their pantheon due to her exceptional foresight.
It was this power of hers that allowed the Asgardians to win countless wars. She even helped them defeat the frost giants and free the nine realms from their grasp. But one night, in her sleep, she saw the destruction of the Asgard and the death of almost all of the gods.
That was the last vision she ever had. Because after she informed Odin about the event called Ragnarok and the catastrophe it would bring forth to the nine realms, she decided she did not wish to live any longer. The Giantess claimed that she had served her purpose and thus now wanted to live the rest of her days in peace.