Sif, I believe, is Odin (the father of the Gods), wife. She has beautiful, long, golden-blond hair.
One night, Loki cut it all up, and made into a wig for his own red headed head.

Odin found out and got EXTREMELY mad! He was about to throw Loki out, when he soon made it up to the Gods (Oh, and may I tell you, Loki is a Giant, that is Shapeshifter. He was good at first, that is why he is with the gods, but by Ragnarok*, he betrays the gods.), by growing REAL gold into Sifs shortened hair, so it was nice and long, and beautiful again.

*The Last Days of the Vikings