From The Saga of King Gautrek.
Alfhild was the daughter of King Alf of Alfheim (the land of the elves). She was carried off by Starkard, a cunning giant renowned for his wisdom.
Alf called on Thor to rescue his daughter. Thor killed the giant and returned Alfhild to her father. Afhild later bore the giant's child and named him Storvirk.
Thor was most put out that Alfhild had slept with the giant but refused him.
(Tales of Thor rescuing women and being rewarded with a night of passion were probably well known, the one surviving example is the tale of Eaglebeak.
This story comes across as a comedy based on an established and clichéd tale type, which must have been a favourite in every weaving room in North Scandinavia.
This tale is continued in the 'The Cursing of Skarkard' which is set two generations later.)