Grump used to serve as Viggo's personal garbage disposal, eating all the scrap iron at the Dragon Auctions on Dragon Hunter Island until he met Gobber. He was taunted and mistreated by every man on the island, especially Ryker, who believed that he'd be more useful as food. But Gobber was quite taken with the large and ungainly dragon, showing Grump some respect for the first time in his life. He asked Ryker if Grump would be auctioned off as well, possibly hoping on bidding for him with Berk's gold. His true strength and potential are revealed when he hears the rocks Gobbber throws as a signal for help, and takes out two underestimating guards. He then frees Gobber and the Dragon Riders from a dragon-proof cage by simply biting the door of their cell right off its hinges. He and Gobber then join the other riders as they fly home to Berk.
Grump and Gobber join the Auxiliary Riders in helping Hiccup take Viggo's base and recover the Dragon Eye.
For the next couple of years, he worked alongside Gobber in his Blacksmith Shop, keeping the forge lit with his fire. He and Gobber also accompanied Stoick and the other Riders on their search for Hiccup and Toothless, and pins Eret to the deck of his ship when they're found. When Hiccup flies off again, he accompanies Stoick and Skullcrusher to chase them down, later finding them in Dragon Mountain with Valka. He hangs out with Gobber, Hiccup, and Toothless, eating Valka's "bad" cooking, while Valka and Stoick dance.
In the battle against Drago, Grump uses his tail bludgeon to bowl through Drago's men and knocking them out. But he eventually becomes incapacitated, leaving Gobber to continue the fight on foot. Grump is taken control of by Drago's Bewilderbeast along side all the other dragons, but is one of the first to snap out of it and join Toothless a defending Berk and its people. After Drago is defeated, Gobber is excited to be reunited with his dragon and tells Grump "Give me a cuddle, Grumpy!", to which Grump happily flies in and pins Gobber to the ground.
Grump's body is covered in copper and grey scales. His ears and teeth appear to be similar to a Gronckle, but that's where the similarities end. His wingspan is much bigger, the bludgeon on his tail is much more round and bulbous, and he has a glazed expression on his face as if he's always half-asleep, which might actually be true, and when awoken by Gobber to heat the fire, he lets it explode. where Gobber comments about: "I'm thinking about letting someone adopt you!"
Personality and Behavior
Grump is extremely lazy and whatever time he doesn't spend sleeping, he spends it eating. However, he is also incredibly loyal to his rider and would do anything to help him. Although Gobber often complains about Grump (very hypocritically), they are still the best of friends and partners.
Skills and Abilities
As a Hotburple, Grump has many abilities much like those of a Gronckle.
Tail Bludgeon: Grump is shown to be able to use his lumpy tail as a powerful melee weapon. He is very talented at this, as he can do it while he's asleep, airborne, carrying Gobber, or any combination of the three.
Jaw Strength: As Ryker stated, Grump's species is the only one strong enough to bite through dragon-proof bars. This also comes in handy when he's eating scrap iron.
Intelligence: Despite being underestimated by the hunters because he's fat and lazy, Grump was able to understand Gobber's plea for help as well as his command to attack the two guards.
Lava Blast: Grump is able to blast lava from his mouth. He uses this ability both in combat and in lighting up Gobber's forge. (and letting it explode)
- The bludgeon on the tip of Grump's tail and Gobber's new, mace-like, hammer-shaped, artificial arm strongly resemble each other.
- Grump often takes Gobber's commands slowly.
- Grump seems to like sleeping on people in How to Train Your Dragon 2, although he is mostly seen sleeping on the ground.
- Grump's laziness is similar to Garfield the Cat's own laziness.
- Grump is the only dragon to have a name before meeting his Rider.