Madguts the Murderous was Chief of the Murderous Tribe and lived in the Murderous Mountains.
Madguts first appeared in A Hero's Guide to Deadly Dragons trying to find the Stealth Dragon, a "Secret Weapon" that Big-Boobied Bertha stole from him. He was going to send her to the Uglithug Slavelands until Hiccup intervened, so he took the Hairy Scary Librarian instead.
Madguts' second appearance, in How to Ride A Dragon's Storm, was his last. Madguts conspired with Norbert the Nutjob to win in the second Inter-Tribal Viking Swimming Race. But Hiccup won instead, stopped the blood feud and made Madguts sing a love song and look like an "ickle pretty shepherdess" at the next Thing.