Halldor

Harald known as Halldor in the English version is the leader and founder of Team Ragnarok competing in the WRGP. He is one of the Holders of the Rune Eye and the owner of "Odin, Father of the Aesir".

Pre-Team Ragnarok
Harald received his Rune Eye while acting as a military pilot. During a flight, he and another comrade were threatened by the mysterious appearance of clouds. While in the storm, unable to see anything, Harald's Rune Eye appeared and with its power allowed him to see through the storm and prevent his comrade from crashing into mountains by using the rockets from his plane. Because of this, he was called in for wasting the material but quit to follow his interest in Norse Mythology.

Long after this event, Harald begin researching about the Norse mythology involving Ragnarok and went on a jounrey to hone his dueling skills and become worthy to own "Odin, Father of the Aesir" which was in a tree root in a chamber beneath his familys mansion. He did as instructerd by Sebastian due to his family's duty.

Harald then began searching for others who might also have a Rune Eye, with the help of his servant Sebastian. This leading him to finding Dragan's father who gave him "Thor, Lord of the Aesir", with the condition of delivering that card to his son. After meeting Dragan, who had survived an avalanche because of the Rune Eye protecting him, Harald convinced him to use "Thor".

Lastly, Harald, along with Brodor, traveled to an island where "Loki, Lord of the Aesir's" card was. Upon finding it, Brave steals it and tries to escape on a boat. As Dragan, Harald and Sebastian follow after him, Brave's boat crashed against a boulder and sent him flying towards a pillar of rock.

However, the final Rune Eye appeared on his eye and a mysterious thunderbolt destroyed the pillar. After the three of them catch up with Brave, he says that the card is his, which Harald's acknowledges, saying that "Loki" has chosen him.

World Racing Grand Prix
Harald, along with his companions, were on a plane flying towards New Domino City for the WRGP finals. At the same time, the Three Pure Nobles achieved Falsification of history. Harald, along with the others noticed that the Aesir had protected them from the wave.

Later, Harald and his team appeared publicly to host an exhibition Duel against the other teams in the WRGP, where Dragan chose to Duel Jack Atlas. During the Duel, after Dragan Summons "Thor, Lord of the Aesir" and attacks "Red Dragon Archfiend", the two monsters emit a strange wave of energy while battling. Because the force began to destroy the building, the Duel was called off.

Before their match against Team 5D's, his comrades witness how the Spiral building is emerging into their world. Yusei Fudo, Jack and Crow Hogan arrive, and Halldor realizes that the Mark of the Dragon allows them to see the building as well. He reveals that they know Team New World are the ones behind the upcoming crisis.

Harald then proceeds to tell them the story behind the Rune Eye, as well as that of the 3 Aesir. After this, Yusei asks him to cooperate with them in stopping Yliaster. However, Harald reveals that the three Aesir do not wish to ally themselves with the Crimson Dragon because Yusei's father had been the one who created the Ener-D reactor and Roman Goodwin caused Zero Reverse and began all this. Because of this, they believe that Yusei himself also carries a destiny of destruction.

Therefore, Harald declares that the semifinals will decide who fights against Yliaster. When Harald finally faces against Yusei in the semifinals, Harald pushes him into a corner as he has all 3 Aesir on the field. Still Yusei, with the power of the Crimson Dragon and "Shooting Star Dragon", was able to defeat him and with this Team Ragnarok loses and Team 5D's proceeds to the finals. After the Duel ends and both duelists get back to the pits, Harald recognizes Yusei's strategy of countering the "Odin's Eye" to win the Duel. He then uses his Rune Eye and notices that behind Yusei and "Shooting Star Dragon" is the Crimson Dragon. Harald takes this as evidence that the Aesir now acknowledge Yusei and his friends as comrades.

After Dragan, Brave, and Sebastian arrive to where he is, Sebastian questions him if they should leave the fate of the world on their hands. Halldor then responds that Yusei's fate won't bring destruction but instead a road to brighter future.

When the Three Pure Nobles appear to the Signers the day previous to the WRGP finals, Halldor and his teammates are also present. They explain to Team 5D's that the fate of the world lies with them winning the match as that would cause the Divine Temple to disappear

Harald and his team watch as Team 5D's defeat Team New World and later congratulate them on their victory. They also witness the appearance of Divine Temple.

Divine Temple
Harald, Dragan, and Brave appear again on their Duel Runners. Brave states that theirs were working because they were using the power of their Rune Eyes. Halldor further explains that they weren't affected by the negative rotation, implying that the Duel Runners of Team 5D's should work because of the power of the Crimson Dragon.

Later on, the team speaks with Yusei alone, stating that they will create a path to the Divine Temple. Harald tells Yusei of the legend of The Rainbow Bridge Bifrost, a path that connects the human world with the the divine world. He explains that he and his teammates will use the energy of the Ener-D Reactor to create and manifest a path on the Daedalus Bridge.

They travel with Yusei and Bruno to the reactor. Connecting their runners to it, the three Summon the Aesirs to increase Ener-D's volume and reverse its rotation. Harald then calls forth Bifrost, creating a path from the Daedalus to the Divine Temple.

As Yusei and his friends travel on the path, Team Ragnarok struggle to maintain the bridge. Eventually, their Valhallanders reach their limits and explode, causing the Aesirs and Bifrost to disappear. In Episode 147, he and his teammates are shown to have survived.

Turbo
Harald plays a Nordic Ascendant Deck, focused on the Summoning of "Odin, Father of the Aesir" and supporting the Aesir monsters of his teammates, which revive at each End Phase if destroyed.

Trivia

 * Harald's Special Summoning of "Nordic Wicked Dragon Jörmungandr" and "Nordic Wicked Wolf Fenrir" to Yusei's side of the field only for Yusei to use them to Summon "Shooting Star Dragon" and beat Harald is highly ironic, due to the fact that, in Norse Mythology, these beasts were foretold to kill Thor and Odin, respectively. The two are in fact the children of Loki.