Sif is a figure in Norse Myth.
Sif is the wife of the Thunder God, Thor, who is the son of the Allfather, Odin, and essentially the Earth in the form of a being. (open to interpretation, as is much in myth and legend)
In a short form...
Sif's hair is vital to Norse Myth, as Loki cuts the hair from Sif's head while she sleeps. Odin demands Loki restores her hair to it's former beauty.
Loki travels to Svartalfheim and asks the Dark Elves to craft hair as fine as Sif's hair from a bar of gold. After many words of praise and promise they forge the hair and give it to Loki. He also requests the spear Gungnir and the ship Skidbladnir as well.
Loki returns and presents the hair on Sif's head and the spear to Odin and the ship to Freyr.
