In Norse Mythology, Andvari is a dwarf. He is capable of turning himself into a fish when needed and possesses the ring Andvaranaut. Living under a waterfall he collected weath with his ring until Loki caught him with a net provided by Ran and forced him to give up his treasure. Andvari tried to keep his ring so he could rebuild his fortune, but Loki made him give it up as well so the dwarf cursed his treasure so anyone who owned it would have disaster come upon them and cursed the ring so anyone who held it would feel pain and have bad luck.

The story of the robbing of Andvari is told in the Reginsmol.

Sources:
http://www.pantheon.org/articles/a/andvari.html