Hreidmar (also spelled Rodmar or Hreithmar), in Norse mythology, the father of Regin, Otter, and Fafnir. In some versions he was a powerful magician, in others, king of the dwarfs. In one story, the gods Odin, Hoenir, and Loki had been traveling together, and Loki had killed an otter who had been eating a salmon, thinking to make a meal of them later. The three 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 the body of his son Otter, he called his other sons, Fafnir and Regin, and they took the gods prisoner.
The gods offered Hreidmar wealth in exchange for their lives. Otter was skinned, and Hreidmar said that the gods' ransom would be the skin filled entirely with gold, inside and out. Loki was sent out to acquire enough gold to do this. He returned with Andvari's hoard, including the ring that Andvari had cursed. The gods gave the gold to Hreidmar to filled the otter skin, all except the ring, which Odin set aside. When the otter skin had been both filled and covered on the outside with gold, Hreidmar examined it closely and saw that one whisker still showed. Unless it was covered entirely, Hreidmar said, 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. Hreidmar accepted it, and the gods were freed.
Loki told Hreidmar that a curse had been attached to the ring, and Hreidmar declared that if he had known about the curse, he would not have agreed to accept the transaction. Then Fafnir and Regin asked their father for a share of the gold, but he would not give them any of it. Fafnir waited until Hreidmar was asleep, then murdered him with a sword, continuing to fulfill the curse that had been put on the ring.