Andvari is the antagonist in the story The Ring of the Nibelungs. He is a shape shifting Dwarf whom Loki seeks out to take treasure from to avenge the death of the Dwarf King's son. Andvari loves hoarding gold and keeps his gold in a giant cave, where he likes to change into fish to swim about and eat other fish.
Andvari is jealous and never likes to leave his gold, and he hates Loki for wanting his gold. Loki demands all the gold but Andvari refuses to let Loki have his Ring.
The Ring is of importance because when the gold gets low, Andvari makes more gold from his Ring, which has supernatural reproducing properties. The Ring is more vital to the hoard than any other bit of treasure. Loki demands the Ring too, but Andvari refuses.
Loki threatens death to Andvari but the Dwarf says that the Ring's reproductive qualities will not work for the god. So, Loki snatches the Ring, and Andvari spits out a curse that any who wear or own the Ring shall die or be killed. Loki is gone after the curse is spoken, and he takes the Ring to the gods. This Ring led to the murder of Baldar.
In an interesting eerie sidenote, the treasure recently found in a German forest was said to be the Nibelung treasure, and thus could contain the curse that Andvari put on it.