Detailed Instructions: In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: This figure exchanges insults with a boatman with a name meaning "Grey-beard" who refuses to ferry. One member of this deity's retinue is in atonement for scraping the marrow out of a thighbone, and the sorceress Groa ran off while healing this son of Fyorgin. This god lifted and brought back a huge brewing-kettle for Aegir. A piece of (*) whetstone was stuck in his head after he got stuck under the corpse of Hrungnir. This employer of the servants Roskva and Thialfi was once at sea with Hymir, who cut his fishing line, and waited until sunlight so the dwarf Alvis would turn to stone. He once disguised himself as a bride and flew in his goat-driven chariot to reclaim a prized weapon. For 10 points, name this Norse god whose use of Mjolnir causes thunder.
A:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Social Science