How to Train Your Dragon: The Hidden World (also known as How to Train Your Dragon 3) is a 2019 American animated fantasy film written and directed by Dean DeBlois, loosely based on the book series by Cressida Cowell. Produced by DreamWorks Animation, it is the sequel to How to Train Your Dragon 2 (2014) and the final installment in the How to Train Your Dragon trilogy. The film stars the voices of Jay Baruchel, America Ferrera, F. Murray Abraham, Cate Blanchett, Gerard Butler, Craig Ferguson, Jonah Hill, Christopher Mintz-Plasse, Kristen Wiig, and Kit Harington. The film follows 21-year-old Hiccup seeking a dragon utopia known as the "Hidden World" while coming to terms with Toothless's new bond with a female Fury, as they deal with the threat of Grimmel the Grisly, a ruthless dragon hunter.

Discussions regarding a third How to Train Your Dragon film began in December 2010, with DeBlois later stating that the second film was being intentionally designed as the second act of a trilogy. The animation challenges of the production required DreamWorks Animation to update and invent new software to handle complex tasks, such as lighting the Light Fury dragon.

How to Train Your Dragon: The Hidden World was released in Australia on January 3, 2019, and in the United States by Universal Pictures on February 22. Like its predecessors, it received critical acclaim, with reviewers considering it a satisfying conclusion to the trilogy, with praise for its animation, voice acting, score, and emotional weight. The film grossed $540 million, and received several accolades, including five Annie Awards nominations, a Golden Globe nomination, and a nomination for Best Animated Feature at the 92nd Academy Awards.

Plot

A year after becoming chieftain,[a] Hiccup, his Night Fury Toothless, and their fellow dragon-riders continue to rescue captured dragons to bring them to Berk. However, the island has become overpopulated with dragons and faces constant attacks by dragon hunters. In response, Hiccup desires to find the "Hidden World", a safe haven for dragons once spoken of by his late father, Stoick. Meanwhile, a white female Light Fury, held captive by warlords, is given to an infamous dragon hunter named Grimmel the Grisly as bait for him to capture Toothless for the warlords' use as an alpha.

Toothless finds the Light Fury in the woods, and they become enchanted until she flees, sensing Hiccup and Astrid nearby. Later, Hiccup and Tuffnut discover Grimmel's dragon traps. That night, Grimmel visits Hiccup, demanding Toothless while boasting of killing nearly every Night Fury to extinction. Hiccup, having prepared an ambush, faces Grimmel, who escapes as his Deathgripper dragons destroy Hiccup's house and Berk. Hiccup then leads the citizens and dragons to seek the Hidden World for safety from hunters.

Mid-journey, the Berkians discover an island on which they initially plan to rest, but soon begin to settle there, dubbing it "New Berk". Seeing Toothless' inability to fly solo hindering his growing relationship with the Light Fury, Hiccup rebuilds an automatic tailfin for him.[b] Upon receiving it, Toothless flies off, meeting up with the Light Fury and flying with her to an unknown land. On a scouting patrol, Valka notices Grimmel's approaching army and reports back to Hiccup. Hiccup and the dragon riders head to capture Grimmel, but fall into his trap and barely escape, except Ruffnut, who irritates Grimmel until he lets her go.

Hiccup, Astrid, and Stormfly search for Toothless and find the Hidden World, where Toothless has become the alpha of the dragons there with the Light Fury as his mate. When the resident dragons spot Hiccup and Astrid, they attack the duo, but Toothless saves them and returns to New Berk. Hiccup realizes that humans would be intruders and are unsafe in the Hidden World. Ruffnut returns but unknowingly leads Grimmel right to them. He captures Toothless and the Light Fury, who had followed Toothless back to the island. Grimmel uses Toothless's alpha status to capture Berk's dragons by threatening to kill the Light Fury if he does not comply.

With Astrid's support, Hiccup joins the dragon riders to thwart Grimmel and his army. They surprise Grimmel's forces while gliding on wingsuits, sparking a battle to rescue the dragons. Hiccup, aided by Stormfly, frees Toothless as Grimmel drugs the Light Fury and flies off with her. Hiccup and Toothless chase Grimmel, defeating his Deathgrippers with lightning, but Grimmel tranquilizes Toothless midair, making him fall. Realizing he needs help, Hiccup frees the Light Fury and urges her to save Toothless before falling with Grimmel towards the ocean. The Light Fury saves Toothless and returns to rescue Hiccup, who removes his prosthetic leg that Grimmel was holding onto before being carried away, leaving him to die from the impact. Back on the island, Toothless and Hiccup acknowledge that dragons are not safe in the human world and that humans are forbidden in the Hidden World. Hiccup shares a heartfelt goodbye with Toothless as the Berkians release their dragons to the Hidden World. Months later, Hiccup and Astrid marry and become New Berk's chieftains.

A decade later, Toothless and the Light Fury have mated and hatched three hybrid dragon fledglings called Night Lights. Hiccup and Astrid, along their daughter and son[c] sail across the sea to visit them at the edge of the Hidden World. After introducing his children to his old friend, Hiccup and Astrid take their children flying on Toothless and Stormfly, accompanied by the Light Fury and their offspring. Hiccup vows that, until humans and dragons are ready to co-exist peacefully, the dragons will stay hidden while the Berkians guard their secret.