Dagur the Deranged is a character that appeared in the Riders of Berk series.

Son of Oswald the Agreeable, he visited the island of Berk (like his father did every year) instead of his father and is the new chief of the Berserkers. His presence in Berk is explained by the peace contract that every year the Berserkers (so, Dagur's vikings) and the Hooligans (Berks' vikings) renew. Dagur, while in Berk, kept insulting his father and looked for dragons to kill. After that Barf and Belch broke into the hall, Dagur led his vikings and captured the dragon, bringing the Zippleback to the arena, since he wanted to kill it with Stoick. Fortunately, the other dragons led an "attack" towards him, driven by their riders and Dagur was forces to flee. He told Gobber, however, to consider the peace contract signed and so, renewed.