Stoick the Vast is the leader of the Viking tribe at the start of How to Train Your Dragon.
Stoick is the chief of Berk, the Viking settlement repeatedly attacked by dragons. He leads the community’s defenses and expects the young Vikings to learn traditional dragon-fighting skills, making Hiccup’s unconventional approach a source of conflict between father and son.
As the film progresses, Stoick sees that Hiccup’s observations about dragons are correct. His leadership therefore changes from resistance to cautious acceptance, helping Berk move toward cooperation with the dragons rather than continued warfare.
This answer is distinct from Hiccup’s name, even though Hiccup later becomes Berk’s chief in the broader story. Gobber is Stoick’s trusted adviser and friend, but he is not the tribe’s leader.