Thor was the strongest of all gods and husband of Sif
Sif was the wife of Thor and had the most beautiful hair
Loki the god of trickery cut off Sif's hair. Thor was going to kill him, but Loki promised him that he would replace Sif's hair.
I'm sorry! I'll replace it!
I'm going to kill you!
Loki went to Ivaldi's sons, and asked them to make new hair for Sif. They complied, eager to win the favor of the gods, and also gave some extra gifts to Loki
Will you please make new hair for Sif?
Of course, but take these gifts for your fellow gods as well
Loki then had an idea. He went to two other dwarves and said, "if your gifts for the gods are better than those from Ivaldi's sons, you can take my head without harming my neck. The dwarves complied, eager to get rid of Loki.
If you craft better gifts, you can take my head!
The second pair of dwarves made 3 gifts, including Thor's hammer. Loki delivered them, and the gods liked them more than the other dwarves's. Howeveer, they could not take Loki's head without damaging his neck. And this is how Thor got his hammer.