In Norse Mythology, Rodmar is the father of Regin, Otter, and Fafnir. In some myths he was a magician with great power and in others he was the king of the dwarfs.

In the best known story involving Rodmar from the Prose Edda, Odin, Loki, and Hoenir were traveling in a group and Loki killed an otter for a meal later in the day. They came upon Rodmar's farm and asked to stay for the night, offering to share the otter for dinner. Rodmar saw the body of his son and had Fafnir and Regin help him take the gods as prisoners.

The gods had Otter skinned and offered Rodmar money as ransom. Rodmar said he would take Otter's skin filled with gold in exchange for their lives. Loki was sent out to find gold for the ransom and returned with Andvari's hoard and Andvaranaut. The gods turned over the treasure to Rodmar after Odin set the ring aside and Rodmar found it covered the skin leaving one whisker showing. He refused to let the gods go until the entire skin was covered, so Odin covered the whisker with the ring and said the ransom had been paid.

Loki then told Rodmar about the curse attached to the ring and Rodmar declared that if he had known he never would have accepted the ring. When the gods left, Fafnir and Regin asked their father for their share of the treasure and he refused. When Rodmar fell asleep, Fafnir murdered him.

Rodmar is also spelled Hreidmar, Hreithmar, and Reidmar.

Sources:
http://www.meta-religion.com/World_Religions/Ancient_religions/Europe/norse_mythology.htm
http://www.search.eb.com/ebi/article?eu=335856&query=hreidmar