In the 2010 film How to Train Your Dragon, Hiccup gives the injured Night Fury the name Toothless.
Hiccup chooses the name after observing the dragon’s retractable teeth. When the Night Fury opens its mouth, its teeth can disappear, making it appear toothless. The name is therefore both a joke and a clue to a distinctive biological feature.
Toothless becomes Hiccup’s companion after Hiccup frees him from a trap rather than killing him. Their relationship drives the film’s central change: Hiccup learns to understand dragons, while Toothless gradually trusts a human. The pair also discover that cooperation is more effective than Berk’s traditional dragon-fighting methods.
Toothless is sometimes confused with the other named dragons in the films. Stormfly belongs to Astrid, Hookfang belongs to Snotlout, and Cloudjumper is associated with Valka. Toothless is specifically Hiccup’s dragon and the story’s principal Night Fury.