Dammen had a brief conflict with the Hooligan Tribe when he kidnapped one of their dragons, a Deadly Nadder named Stormfly. After the assault on his "ice castle," his captive dragons were freed and he was apprehended.
Arngrim first appeared in "The Ice Castle", sailing towards Berk, and catching sight of the Dragon Riders. After acquainting himself with the villagers, Arngrim offers to sell some of his furs to them. Much softer and warmer than the ones they have, everyone takes a liking to the trader; except Gobber, who had a run-in with Northlanders in the past. Arngrim takes an interest in the dragons, especially Stormfly, which makes Astrid suspicious of him.
Later that night, after the Vikings have fallen asleep, Arngrim lures Stormfly to his ship and captures her. He soon makes his escape. He sails to the Ice Needles, a large glacier fortress, to carry out his main goal.
The Dragon Riders manage to track Arngrim down and discover he plans to sell dragon and their eggs to his buyers, thinking they will be able to control them from an early age at his Dragon Auction. Hiccup and Toothless flew in to the auction showing that while dragons can be trained, they cannot be domesticated, releasing the Boneknapper and Timberjack he had in chains. However, one of Toothless' blasts incubates a Whispering Death egg, thus allowing it to hatch. After Hiccup trains the hatchling and Astrid gets Stormfly back, the Vikings corner Arngrim and force him to surrender.
Dammen is described to be a trader with no conscience, and is shown to go to devious means to get what he wants. He would resort to kidnapping dragons in order to have a supply for his dragon auctions.
Cunning and witty, he tricks others into liking him by offering them his goods. This causes them to lower their guard and allow him to achieve his undesirable goals.
Dammen is a bulky, tall Viking. He sports a shaggy beard, two locks at the end bound in red and green bangles. They are often coated in frost due to the low temperatures of his homeland. Instead of a helmet, Dammen wears a skull on his head. As a trader, he wore a fur hat. He also wears a thick red fur jacket and has red gauntlets that stretch to his wrists.
- Dammen is the second trader seen in the franchise, with the first being Johann.
- However, Dammen is evil, while Johann is a friend to Berk and the Dragon Riders.
- Like Valka, Dammen appears to be able to estimate a dragon's age, guessing Stormfly was a two-year-old.
- However, it is unknown if he actually knew Stormfly's age or if he was just guessing.
- Some of the other eggs Dammen tried to sell belonged to Deadly Nadders, Thunderdrums, Monstrous Nightmares, and Snaptrappers.