Not much is known about Chucklehead, but he was described as being the spitting image of Thugheart, who in turn was the spitting image of Grimbeard the Ghastly. He was incredibly stupid, and loved his brother Hiccup Horrendous Haddock II dearly, unlike their eldest brother Thugheart. After Hiccup II's death and Thugheart's banishment, Grimbeard's kingdom fell and he returned to Berk which then made Chucklehead the new chieftain. Chucklehead eventually married Buffintruda and had two children. Chucklehead later died of old age.
Chucklehead is an ancestor of Stoick the Vast, Hiccup Horrendous Haddock III, Baggybum the Beerbelly, and Snotface Snotlout. So despite having little background about him, Chucklhead is still one of the most important characters in the series as he has many significant descendents, including the series protagonist, Hiccup.