In a mythical Viking world, a young Viking teenager named Hiccup aspires to follow his tribe's tradition of becoming a dragon slayer. Living on the island of Berk, where battling dragons is a way of life, Hiccup is considered weak and ineffectual by his tribe and especially by his chieftain father, Stoick the Vast. Despite his intentions, Hiccup's unconventional and inventive approaches don't fit the brute-force methods favored by his fellow Vikings.

During one of the frequent dragon raids, Hiccup manages to shoot down a rare and feared Night Fury dragon with a bolas cannon he invented, but no one believes him. He later finds the dragon in the forest, trapped and injured. Unable to kill the defenseless creature, Hiccup forms an unlikely friendship with the dragon, which he names Toothless. As Hiccup learns more about dragons through his secret interactions with Toothless, he begins to challenge the long-standing prejudices held by his people, including his own initial perceptions. Through his connection with Toothless, Hiccup develops novel dragon-fighting techniques that impress his peers, who are unaware of his new friend. His innovative methods starkly contrast the brutal and simplistic tactics the Vikings have always used.