An excerpt from Skaldskaparmal (http://www.angelfire.com/on/Wodensharrow/skaldskaparmal.html)
'What is the reason for calling gold "otter's ransom?
'It is said that when the Æsir, Óğin and Loki and Hnir were exploring the whole world, they came to a river and went along it to a waterfall, and by the waterfall was an otter which was eating a salmon it had caught there and it was half-asleep. Loki picked up a stone and flung it at the otter, striking it on the head. Then Loki boasted of his catch - with one throw he had bagged an otter and a salmon. They took the salmon and the otter away with them and came to a farm which they entered. The farmer living there was called Hreiğmar. He was a powerful man with much skill in magic. The Æsir asked the farmer for lodgings there for the night, saying that they had plenty of food, and they showed him their catch. When Hreiğmar saw the otter, however, he called his sons Fáfrir and Regin, and told them that their brother, Otter (that is, he was able to change into an otter), had been killed, and also who had done the deed. Then father and sons attacked the Æsir and made them prisoner and bound them, telling them that the Otter was Hreiğmar's son. The Æsir offered to pay as large a ransom as Hreiğmar himself should demand, and those terms were agreed on and confirmed by oath. Then the otter was flayed, and Hreiğmar took the skin and told them that they had to fill it and completely cover it into the bargain with red gold. That would reconcile them. Óğin then sent Loki to the World-of-dark-elves, and he came to the dwarf called Andvari. He was in a pool in his fish shape, and Loki seizing him exacted as ransom all the gold he had in his rock dwelling. When they got there the dwarf produced all the gold he possessed and it was a very great sum of money, but he kept back in his hand a little gold ring. Loki noticed this and told him to give him the ring. The dwarf begged him not to take it from him, saying that if only he were allowed to keep it he could by its means become wealthy again. Loki said that he was to be left without a single penny and taking the ring from him was going away, when the dwarf declared that the ring would destroy everyone who owned it. Loki replied that that was all to the good, adding that the prophecy should be fulfilled, provided that he himself pronounced it in the ears of those about to take over the ring.
'He went away and came to Hreiğmar and showed the gold ring to Oğin. When Óğin saw it he admired it for its beauty and kept it back, although he paid the gold to Hreiğmar. Hreiğmar stuffed the skin to bursting and when it was full raised it up on end. Then Óğin went up to it to cover it with gold and, this done, he asked Hreiğmar to look and see if the skin was not completely hidden. Hreiğmar took a good look at it and caught sight of one whisker. He ordered this to be concealed or otherwise, he said, their agreement would be at an end. Then Oğin drew the ring from his finger and concealed the whisker, saying that now they had paid the otter's ransom. When, however, Óğin had taken his spear and Loki his shoes and there was no reason they should be afraid, Loki declared that what Andvari had said should hold good, that that ring and that gold would destroy whosoever owned them. That has been the case ever since. Now you know why gold is called otter's ransom or the forced payment of the Æsir or metal-of-strife.'
'Is anything more known about this gold?'
-Of Fáfnir, Regin and Sigurğ-
'Hreiğmar accepted the gold as ransom for his son, and Fáfnir and Regin asked for some of it as a ransom for their brother. Hreiómar did not give them a single penny of it. The brothers were wicked enough to kill their father for the gold. Then Regin asked Fáfnir to go shares in the gold, but Fáfnir replied that there was little likelihood that he would share with his brother the gold for which he had killed his father, and he told Regin to go away or else he would meet with Hreiğmar's fate. Fáfnir had taken a helmet which had been Hreiğmar's and was wearing it; this struck fear into all beholders and was called the helmet of terror. He also had the sword known as Hrotti. Regin owned a sword called Refil. He took to flight but Fáfnir went up on to Gnita Heath and, making a lair there, turned himself into a dragon and lay down on the gold.