Groa is an interesting character from the Eddas. She appears in both the Prose Edda, Skaldskaparmal, and the Poetic Edda, Svipdagsmal. Groa is the wife of Aurvandil the bold, and a powerful Volva. After Thor's battle with Hrungnir, Groa uses her seidr to extract the piece of Whetstone that became lodged in his head when it was shattered by mjollnir. Thor is so happy that he decides to tell Groa that he helped her husband Aurvandil cross the river Elivagar, and that he was now safely home. Unfortunately for Thor she becomes so distracted that her spell stops working and the whetstone remains lodged in his head.
In Svipdagsmal, Svipdag summons his dead mother Groa from her grave mound to help him with a task that his step mother gave him. Even in death she is powerful and she helps her son succeed.