In the How to Train Your Dragon films, Hiccup is the village blacksmith’s assistant who loses a leg.
Hiccup works with Gobber in the forge on Berk and uses his mechanical skills to design equipment, including the prosthetic tail that allows Toothless to fly. During the first film’s final battle, Hiccup loses part of his left leg, and later stories show him using a prosthetic replacement.
The injury is an important visual marker of Hiccup’s development. Rather than treating it as the end of his abilities, the films connect it to his inventiveness and to his partnership with Toothless, whose own damaged tail requires a matching device.
This detail belongs to the film version of Hiccup. Cressida Cowell’s original books depict a different character design and continuity, so details about the film character should not automatically be applied to the novels.