Gustav Larson is the son Mrs. Larson, who first appeared in Gem of a Different Color. He is the first notable character in the franchise to be a child. He was named the Dragon Academy's junior-apprentice-auxiliary-reserve-back-up-replacement-rider-in training-fourth class by Hiccup.
Although young at heart, he shows a loyalty and faithfulness to his mother, despite the fact that she had traded him for a "Stone of Good Fortune" and still remained close with her. This trait rubs off on his dragon, Fanghook, as he is loyal to Gustav. He admires Snotlout and his ability to train a dragon to the point where he gets his own dragon named Fanghook in The Flight Stuff. Gustav oftentimes mimics Snotlout's personality, although he is easily scared, mostly because he is younger, as shown twice to run away: once in Gem of a Different Color and he attempted to flee in The Flight Stuff, although he was stopped by Snotlout
Although much too young, he wants to become a Dragon Trainer and often sneaks in to the Training Academy to play. Even though he and his dragon, Fanghook, got off on the wrong start, both dragon and trainer show a close bond with each other.
In Dragons: Riders of BerkEdit
In Gem of a Different Color, Gustav was traded by his mother to Snotlout for a "Stone of Good Fortune" (Actually a Changewing egg). Snotlout had the boy work as his assistant, with Gustav starting to act like him. He was later ordered to return to his mother by an angry Fishlegs. He is obviously at an impressionable age. He quickly picks up on Snotlout's way of speaking and acting. With Snotlout as his role model, Gustav quickly begins to annoy the other teens. When Fishlegs orders him to return to his mother, he does so in tears. The whole ordeal of being sold and having angry dragons attack his island obviously weighed heavily on him.
In Dragons: Defenders of BerkEdit
Gustav briefly appears in Fright of Passage when he is allowed into the bunker by Ruffnut and Tuffnut, much to Snotlout's apparent dismay and annoyance.
Gustav has a prominent role in the 12th episode of Defenders of Berk, The Flight Stuff, where he gets his own dragon, a Monstrous Nightmare named Fanghook, who is a played name of Hookfang. The reason he gets Fanghook is because after Snotlout tried to train Gustav to ride Hookfang and Hiccup pretended to encourage Gustav to do so, he started to feel unhappy about not being a true dragon rider with his own dragon. After Hiccup and Fishlegs tell him that he needs experience to be a true dragon rider, he went looking for a dragon of his own preference and settled on Fanghook. This ends with him seeming to give up Fanghook but fakes it to Hiccup and Snotlout and continues to train Fanghook afterwards in secret.
In Frozen, Gustav functioned as Snotlout's arms and legs when he was paralyzed by the Speed Stingers, calling themselves "Guslout." He helped steer Hookfang and showed the riders the cave where the Stingers were.
Gustav is the youngest Trainer at the Academy, and one could argue he is not the greatest either. Though he did learn some things from Snotlout. This led into him training Fangook.
Dragon Training and riding: Gustav is, as mentioned above, the youngest trainer at the Academy. When Snotlout was convinced he was going to die, he decided to recruit Gustav. Snotlout taught him about Hookfang, 'the most lethal dragon in the known world'. Gustav, however, wasn't very great at this. Snotlout did teach him enough to succeed at training his own dragon, a Nightmare named Fanghook.
Fanghook: Gustav first encounters Fanghook when the dragon was hunting boars for food. He throws food in his face and fanghook chases him.
After Gustav manages to get his attention, he attacks Gustav. After a while, they bond enough for Gustav to get on his back (although he was still too small to sit tight properly, especially without a saddle). After he and Fanghook help on the scouting mission, Hiccup tells him to release Fanghook into the wild, in which Fanghook unwillingly obligates, which saddens him and his dragon. After Hiccup and Snotlout leave, Gustav calls his dragon back and continues to train him in secret. Fanghook shows affection for Gustav by biting him, but not enough to hurt the young boy.
Mrs. Larson: Gustav is shown to have a close relationship with his mother. He remained loyal and obedient to her despite the fact that she had traded him for the Stone of Good Fortune.
Snotlout Jorgenson: Gustav is shown to admire Snotlout, oftentimes mimicking his action and personality. He showed extreme loyalty to him when he was traded from his mother. Snotlout stated that he had grown to like Gustav, even to the point of entrusting Hookfang to him when he thought he was going to die and training him. Snotlout grew annoyed when Gustav began to "replace" him and was not hesitant to throw him out; however, Snotlout was there to comfort him (in the Snotlout way), when Gustav became frightened after being caught in Dagur's trap.
Hookfang: When Snotlout was convinced he was gonna die, he wanted to train Gustav to ride Hookfang, becoming his replacement in the Academy. Though Gustav really did his best and was shown to like Hookfang, this plan didn't work. This lead him to finding and training Fanghook.
His dragon, Fanghook, is named after Hookfang, which is Snotlout's dragon.
Due to the error in RoB ep 18, it is believed that Gustav and Hildegard were siblings. This is incorrect, as their mothers have different character designs. Gustav's mother incorrectly said Hildegard was her baby, though the two moms were both seen earlier.
Gustav is the youngest dragon rider, though he is unofficially part of the Dragon Academy
He is the second person to have a dragon who is not in the Dragon Academy.
Like Astrid and Hildegard, Gustav's name is one of the few young villagers who's name isn't an insult.
Gustav has the same helmet and vest as Snotlout. The stitching on his tunic is the same pattern as Hiccup's.
At first glance, he looks like a miniature version of Hiccup.