As shown in "Crushing It", Skullcrusher was the first Rumblehorn found by Berk's Dragon Riders on Dragon's Edge. They believed that he was trying to destroy the Edge and drive them out, when in reality he was attempting to warn the riders of an incoming tidal wave. They spent some time trying to catch and relocate him until Stoick came to help and realized that he wasn't interested in destruction. Together with Stoick and the Riders, they were able to save the outpost from being wiped out, with the Rumblehorn proving particularly useful in completing the stone wall that had once been erected to keep him out. Stoick then named him Skullcrusher- on account of their mutual hard heads- and took him to Berk with him. He was also given Thornado's saddle, which was later upgraded by Stoick.
In "Team Astrid", as Stoick's dragon, he defended Berk when Dagur attacked. Skullcrusher then went with Stoick, Astrid, and Stormfly to aid Hiccup in defending Dragon's Edge. He and Stoick charged through a Berserker ship and sunk it before they got caught in one of the nets. However, Stoick was able to free him and then fought alongside the Dragon Riders' Auxiliary, driving Dagur away.
During the events of "Turn and Burn", Skullcrusher then assisted Stoick in tracking down Spitelout when he went missing for a month. Together, along with Hiccup, Snotlout and their dragons, they found him and Kingstail on Storehouse Island. However, they came under attack by the Singetail. They were unable to drive it away and were forced to give up the island when other Singetails arrived. Before leaving, Skullcrusher and Stoick took the "S" from the storehouse.
Stoick and Skullcrusher are shown to be close, with Stoick being comfortable riding Skullcrusher alongside Grump and Gobber.
When Hiccup went with Toothless to try and reason with Drago Bludvist, Skullcrusher helped Stoick, Gobber and Grump to track down Hiccup. They were then able to find Hiccup and encountered Stoick's wife, Valka at her mountain. He, along with Stoick, Hiccup, Gobber, Valka, and their dragons then defended the mountains against Drago's Army.
Following Stoick's death, Hiccup suggests that Skullcrusher pass into the care of their new ally and former dragon-trapper Eret, Son of Eret, recognizing Eret's skill and courage in helping Berk defeat Drago Bludvist. After Drago's defeat, he and Eret then took part in Berks Dragon Races.
Being Eret's New Steed
Appearance and Behavior
In comparison to Grump, Skullcrusher is stern and serious looking, and sometimes a little stubborn, (corresponding with the personality of Stoick). He looks like a cross between a Triceratops and a scarab beetle (due to his neck plates). He always has his nose to the ground, following a scent, as is typical for his species.
He can be friendly, especially towards his rider. He is doggedly determined once he has caught a scent. He is caring and a natural leader, warning the other dragons of an oncoming tsunami to ensure their safety.
Skullcrusher also has a playful side, like spinning around while flying. He was also see playing a bit with Toothless.
- Tracking: Like all Rumblehorns, Skullcrusher has a keen sense of smell, enabling him to track anything once he has caught the scent.
- Strength: Skullcrusher is extremely strong and quite capable of destroying any dragon traps he encounters using his tail and jaws. Skullcrusher can charge with his head lowered and horns displayed to do some serious damages. He also doesn't have trouble carrying large Vikings on his back such as Stoick and extra weight of Hiccup. Skullcrusher's extreme strength was greatly proven when he was able to ram down a sea stack when flying at full speed towards it, as well as during the time when he charged clear through a Berserker ship and sunk it into the ocean.
- Endurance: Skullcrusher is able to recover quickly after being directly hit by a Singetail's fireball.
- Fire: Skullcrusher can shoot burning, explosive missiles from his mouth that can do a lot of damage.
- Acrobatics: Skullcrusher has some impressive agility in the air despite his size.
- Speed: Skullcrusher is also surprisingly quick on his feet and in the air.
- Intelligence: Skullcrusher has shown to be able to try to figure out ways to make other dragons to flee the island before they could be killed.
- An image error in Empire Magazine led to believe that the Thornridge was a new dragon species with the same name. The description and combination of animals was indeed about the Rumblehorn.
- Along with Thornado, he is the first Dragon whose current/former rider is deceased.
- He is the first Dragon who had more than one rider, excluding Barf and Belch.