In Norse mythology, Andvari was a dwarf. He lived underneath a waterfall. He had the power to change himself into a fish at will. He had a magical ring named Andvaranaut, which helped him become wealthy. In Wagner's version he is known as Alberich.
Loki caught him (with a net provided by Ran) and forced him to give up his gold and Andvarinaut. Andvari cursed Andvaranaut with the threat that it would destroy whoever owned it, leading (inevitably) to much misfortune.
See also: Sigurd, Brunhilde, Fafnir, Hreidmar
