Otter (also spelled Otr), in Norse mythology, a son of Hreidmar (Rodmar), and brother of Regin and Fafnir. His death indirectly set in motion the curse of the Nibelung ring. Otter often came to the waterfall of Andvari, who hoarded gold, in the shape of an otter. One day he had caught a salmon there and was eating it with his eyes half-closed when the trickster god Loki threw a stone at him and killed him.
Loki was pleased that he had caught both otter and salmon in one blow. The gods Odin, Hoenir, and Loki had been traveling together, and they picked up the dead otter and the salmon, thinking to make a meal of them later. They came to a farm owned by Hreidmar. According to the 'Prose (or Younger) Edda', the gods asked if they could stay the night, and offered to share their dinner. When Hreidmar saw his son Otter's body, he called his sons Fafnir and Regin and they took the gods prisoner.
The gods offered a ransom for their lives. Otter was skinned, and Hreidmar told the gods that he would only free them if they would fill the skin entirely, inside and out, with gold. This would take a lot of gold indeed, since Otter's skin had the ability to stretch magically to huge proportions. Loki was sent out to acquire enough gold for the ransom. He returned with Andvari's hoard, including the ring that Andvari had cursed. The gods gave the gold to Hreidmar, who filled the otter skin, but Odin held back the ring. When the otter skin had been both filled and covered with gold, Hreidmar examined it closely: he declared that one whisker still showed, and unless it was covered, he would not let the gods go. So Odin took out the ring and covered the whisker and declared that the ransom had now been paid. Subsequently, the curse of the ring was fulfilled when Hreidmar was killed by his son Fafnir for the gold. In Norse poetry, a phrase meaning "otter-payment" is a reference to gold.