Gefion is a giant goddess of fertility. She married Skiold, and they had four sons. Gefion was promised by the gods that she could have as much land as she could plow in one day, so she turned her sons into oxen, and pulled the kingdom of King Gylfi into the sea where it became known as Seeland, and took the former lands of King Gylfi as her own. Gefion is the ancestor of the Danes.
Another Gefion is an attendant of Frigg, and is in charge of women who died unmarried. This Gefion may be the same as the one above.