In “How to Train Your Dragon,” Toothless is the dragon Hiccup befriends. Toothless is a Night Fury, a rare and exceptionally fast dragon that Hiccup shoots down while defending Berk from a nighttime dragon attack.
Hiccup finds the injured dragon trapped in a hidden cove and discovers that he cannot fly because part of his tail fin is missing. Instead of killing him, Hiccup gradually earns his trust and builds a harness and prosthetic fin. The two become flying partners, with Hiccup controlling the fin while Toothless provides the strength and movement.
Hiccup names him Toothless because his retractable teeth are difficult to see. Their friendship changes Hiccup’s understanding of dragons: rather than mindless monsters, they are intelligent creatures responding to fear, hunger, and control by larger dragons.
Stormfly, Hookfang, and Meatlug are other dragons ridden by Hiccup’s friends. Toothless is specifically Hiccup’s companion and later becomes the leader of the dragons living peacefully alongside the people of Berk.