In Norse mythology, Andvari (Old Norse "careful one") is a dwarf who lives underneath a waterfall and has the power to change himself into a fish at will. Andvari had a magical ring Andvarinaut, which helped him become wealthy.
Using a net provided by Ran, Loki catches him as a pike and forces him to give up his gold and Andvarinaut. Andvari cursed the stolen gold which would destroy anyone who possessed it. After the deaths of Brynhild and Sigurd, Gunnar left Andvari's gold in a cave. Years later, Andvari discovered the cave and his lost gold, although his ring was lost forever.
In Richard Wagner's cycle of music dramas, Der Ring des Nibelungen, the character Alberich is based in some part on Andvari, but more on the Frankish sorcerer Alberich. The story is also said to have been a source of inspiration for Tolkien's The Lord of the Rings.