Furious is a Seadragonus Giganticus Maximus and the main antagonist in the last HTTYD books
Furious is the dragon-brother of Hiccup Horrendous Haddock II who grew up with him with the Grimler Dragons. He only appears in How to Break a Dragon's Heart and the following books. His fire is believed to be the darkest of any dragon's breath. It is explosive when it comes in contact to with an object. Before the events of the story, Furious was adopted by the two Grimler Dragons who adopted Hiccup II. They grew up together and were caught by a Hooligan hunting party. After Hiccup II reached manhood, he asked Furious to lead the Dragon Rebellion. After Hiccup's death, Furious was caught and imprisoned in Beserk.He was then freed by Hiccup Horrendous Haddock III,but shortly after he betrayed him and started a dragon rebellion againts humanity in a way similar to Alduin.When Furious and his dragon army arrive the war begins but Hiccup has been exiled from his tribe because he has the slave mark.He then seeks out to search for the Dragon Jewel which is believed to put an end to the war.