Gobber: "Do you auction off the ugly, fat one as well?"
Ryker: "Who would buy him? Besides, he eats all the scrap iron and is the only dragon that can bite through a dragon-proof cage. Personally, I'd just as soon skin him and eat him. That fat would be tasty on toast squares with some yak butter. Eh, Grump? But Viggo likes having him around. Says there's a use for everyone."[src]
In "Last Auction Heroes", 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 Gobber 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.
Come on. Get over here, you lazy beast! Where ya goin'? I'm over here![src]
Grump doesn't appear in "The Wings of War, Part 1", but is mentioned by Stoick who calls him "lazy". Gobber is quick to come to his defense, saying he's not lazy, only cautious.
Grump accompanies the Berk Fleet to Dragon's Edge to take it back from the Dragon Flyers in "The Wings of War, Part 2", though his only real act during the battle is to briefly take off before landing again on top of Gobber.
Grump, Gobber, Kingstail, Spitelout, Fanghook, and Gustav rush in to rescue Stoick and Skullcrusher after the two were ambushed by Dragon Flyers in "Darkest Night". Grump ward off some of the Flyers with his lava blast before carrying Skullcrusher back to Berk. He later on appears in Fishlegs' vision of a peaceful Berk, happily running alongside an enlightened Gobber.
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 Valka's 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 alongside all the other dragons, but is one of the first to snap out of it and join Toothless in 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.
Gru-ump! Oh, Grumpy! Time to light the forge![src]
Grump is seen sleeping in Gobber's blacksmith, refusing to wake up when Gobber asks him to light the forge. Bonesnarl then comes and roars at Grump, startling him. He then fires a full blast at the forge.
While the Dragon Riders and other dragons fought off frenzied Silkspanners, Grump mostly slept. He transported Gobber first to Dragon Vine Island where dragonvine threatened a group of farmers, then again back to the island with Silkspanners to investigate. Grump napped as Toothless became poisoned from dragonvine, then healed by baby Silkspanners. He then transported Gobber back to Dragon Vine Island.
After Gobber is forced to take a bath, Grump runs away because of his flowery smell. The player is asked to search for him and he/she finds him on a sea stack near Berk.
Grump's body is covered in copper and grey scales. He has a glazed expression on his face as if he's always half-asleep, which might actually be true.
Personality and Behavior
Grump ain't lazy. He's cautious. There's a difference.[src]
Grump is extremely lazy and whatever time he doesn't spend sleeping, he spends eating. However, he is also incredibly loyal to his rider and would do anything to help him. Unfortunately, he tends to take Gobber's commands very slowly. Although Gobber often complains about Grump (very hypocritically), they are still the best of friends and partners.
Abilities and Skills
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.
Combat and Strength: Despite his sluggish behavior, Grump is a very strong dragon and can become a fearsome adversary when he needs to be. He could ram and knock down Dragon Hunters with little effort, carry multiple humans on his back, and he is able to singlehandedly carry Skullcrusher, a dragon larger than himself, with his claws.
Jaw Strength: As Ryker stated in "Last Auction Heroes", 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).