Andvari is a Dwarf who appears in the Magnus Chase series. He is very old and skilled with magic. He has a large amount of treasure with him and a magic ring which controls that treasure. Andvari now stays in Alfheim, in a lake, as a fish.
Andvari used to live in a cave behind a waterfall. Loki once fished him using a net from Ran and demanded gold to pay off his wergild for killing Órt. Andvari warns him about the treasure and the ring, Andvaranaut, that he just cursed but Loki takes it anyway. The ring eventually turned Órt's brother, Fafnir, into a dragon who was defeated by Sigurd. Sigurd gave the ring to Brynhildr, Queen Grimhild of the Nibelungs then manipulated Sigurd and Brynhildr into marrying her children instead of each other, bringing Andvaranaut's curse into her family. Although the rest of the gold was eventually returned to Andvari by Gunnar, Grimhild's son, Andvaranaut was lost.
Magnus Chase and Hearthstone set out to find him to steal his treasure so they can pay off Alderman's wergild for Andiron's death. After Hearth lifts a river and Magnus reads all the fish's minds and finds the dwarf. He changes back into his original form and, after interrogation, gives them his treasure and ring. He warns them of the curse placed on his treasure about death coming afterwards. He reveals that the ring bounced across the Nine Worlds, once falling to the hands of people who won the Powerball lottery, until it finally came back to him. Nonetheless, Magnus and Hearth took the gold and ring because they needed to save Blitzen after he was stabbed by Skofnung. Andvari jumped back into the pond and disappeared.
Andvari is mentioned when Magnus, Hearth and Blitzen go back to Alfheim to slay Alderman and get Bolverk's whetstone. After they obtain the gold, they return it all, including the ring, to the lake where they found it. But they think that Andvari may have moved someplace else.
In dwarf form, Andvari was tiny for a dwarf. He wore a fish-skin tunic and underwear that was basically a moss diaper. Slime coated his limbs. His stubby arms couldn't hurt Magnus a bit. His face looked like a wrinkly, discolored, gross thumb after it was under a wet bandage for so long. He had scraggly white whiskers and mold-green eyes.
- Shapeshifting: Andvari has the ability to change himself into any kind fish at will.