A silent, intimidating character, Madguts never utters a single word, having his assistant Gumboil translate his grunts for him. He has an arsenal of famous axes, swords, spears and other weapons that Gumboil also carries for him. The most famous is the Number Six Sword, a giant black sword with a skull on its handle. It is one of the scariest, sharpest and feared swords of all time, ranked with Grimbeard the Ghastly's Stormblade.
Madguts is first mentioned in Book 4 by Camicazi. She relates her excellent burglary skill to Hiccup, stating that she had "stolen the helmet right off the head of Madguts the Murderous".
Big-Boobied Bertha, somewhat foolishly, steals Madguts's prize Stealth Dragon in secret to win a bet with Stoick the Vast, the dragon is later stolen by her daughter Camicazi to carry herself, Fishlegs and Hiccup on a secret mission to the Meathead Public Library to steal a copy of How To Train Your Dragon. Madguts is furious, but at the end of the novel Hiccup manages to blame the theft on the Hairy Scary Librarian, whom Madguts takes prisoner and ships off to the Ugli Lowlands.
He is seen raiding the island of Forget Me with fifty troops. At the end, he gives his famous Number Six Sword to Big-Boobied Bertha as a gift.
He is seen with Norbert the Nutjob on the The American Dream 2 after tricking Stoick and Bertha to go back to shore first after Gumboil told them about the deepest purple Fleshfang oil and the race hasn't started till they start swimming. It was part of his plan to get revenge on the Hooligan tribe during the Intertribal swimming race. His ancestor Murderous the Magnificent won the race and become king of the archipelago (With the tribe believing that Grimbeard died in the waves) however after three months, five days and six hours later Grimbeard became the winner of said race and demanded that Murderous be sacrificed to the sky dragons. The annual tribal swimming race has been held every year do to this historic event (though it became a friendly competition). He was going to have Stoick and Bertha sacrifice to the sky dragons. (The judge managed to convince him to wait for the same time that Grimbeard return). And to the shock of the crow they (Hiccup, Fishlegs and Camicazi) did. When Hiccup was ask what should happen to Madguts, he decided to just have him sing a love song to the next tribe leader meet, dressed as a shepherdess (Not wanting history to repeat itself.)