He imprisoned Camicazi in a tree trunk cell. He decided to sacrifice Hiccup and Fishlegs (he believed they were Tantrum's fiancés sent by UG) to the Beast. He also mocked Fishlegs when the latter claimed to be a Berserk, who, in response, said he was only a runt. He was also a bit cross with Hiccup, who claimed Toothless was magic, in which the Chief stated that himself was magic. He had them locked away. The Chief is not seen again until near the end of the book, when he commanded the sacrifice. Hiccup, however, struck a deal with the Beast, and threatened the Berserks to free the prisoners. The Chief instead prepared to attack, until the now freed Camicazi held him hostage at knife. The prisoners were freed, but the Beast burned Berserk's woods anyway. The Chief is not seen again after this, but it's most likely he fled with his Tribe and sailed away, never to be seen again.
As his name entails, he is insane.
The unnamed Chief is described as a gigantic man with lots of chains, manacles, and shackles. He has a bushy wild beard and wears a black helmet with drill spikes sticking out.