Nearly three decades after “The Simpsons” became a fixture on Fox, Bart Simpson is still 10 years old. Call it “the Peter Pan effect”: a never-grow-up miracle in which hand-drawn characters defy age in a way that flesh-and-blood actors find impossible. And then there’s DreamWorks Animation’s “How to Train Your Dragon” series, which has taken another path entirely, allowing its heroes — a band of misfit Vikings who’ve learned to coexist with the creatures they once feared most — to evolve as human beings, resulting in one of the greatest character arcs animation has ever seen.

Hiccup, who first appeared as an awkward teen (designed to resemble gangly Canadian actor Jay Baruchel, who voices him), has grown into a confident Viking leader for the island of Berk, John Krasinski-esque in appearance: strong, strapping, and beardless no more. The one constant through this process has been his friendship with Toothless, the sleek, obsidian-skinned Night Fury — a bat-winged Black Stallion, with a mix of dog- and cat-like qualities bred into its fantasy-pet personality — long believed to be the last of his particular species of dragon.

While not quite the “Boyhood” of animated movies (that time-lapse approach doesn’t really translate to the medium), “How to Train Your Dragon: The Hidden World” packs the emotional heft of the dozen or so years it has taken to get this far, tracking the loss of one parent, the discovery of another, and several momentous lessons in bravery and loyalty along the way. So, although “How to Train Your Dragon: The Hidden World” may be the third film in DreamWorks’ series, in many ways, it’s a first: After getting the greenlight to continue the saga, writer-director Dean DeBlois conceived installments two and three together, constructing a trilogy that enriches the original while also serving to entertain newcomers who know none of the backstory — and that’s key, considering that box office dipped nearly 20% between “How to Train Your Dragon” (DWA’s most successful non-“Shrek” feature) and its sequel, and the studio needs to regain some of that audience this time around.

To that end, “Hidden World” introduces a sparkling white female dragon — dubbed a Light Fury by Hiccup’s friend Astrid (America Ferrera) — to complicate Hiccup’s connection with Toothless, who serves as the alpha to Berk’s entire dragon population, and to introduce fresh conflict into their unique interspecies friendship. Now that humans and dragons have found a way to cohabitate peacefully on Berk, the greatest threat to their community comes in the form of poachers and a new villain, Grimmel (F. Murray Abraham), who’s determined to hunt down and exterminate every last Night Fury.

Though it generates a couple swashbuckling set-pieces — the first of which features an elaborate “oner” as the Vikings liberate the captive dragons from an atmospherically befogged pirate ship — the poacher plot seems a little unnecessary, serving mostly to make the film feel a bit more grown-up than those that have come before. Clad in dragon-scale armor, his renegade silhouette suggesting a guerrilla in the mist, Hiccup brandishes a flaming sword that’s like this series’ version of a lightsaber. The original “Star Wars” trilogy is clearly an inspiration for these movies, with their parental revelations and monomythic hero quests, although DeBlois knows better than to wrap things up with an Ewok jamboree.

Instead of piling on lots of new characters, “Hidden World” expands the geographical scope of their universe. Hiccup has always shown a knack for exploring beyond the borders of Berk’s maps — that’s how he discovered Toothless in the first place — and now, that quality will be the one that could save his clan from Grimmel’s violent schemes. That leaves room for DeBlois to further develop the existing ensemble, crafting a parallel romance for Hiccup and Astrid (America Ferrera) — who’ve enjoyed a slow-burning, semi-competitive flirtation from the beginning — alongside Toothless’ crush on the Light Fury, dazzled as he is to find a blue-eyed, alabaster-skinned female dragon whose hide glimmers like the vampires from “Twilight” when the sun hits it just right.

The film also does right by Hiccup’s friends, leaning on them for comedic relief, as show-offy Snotlout (Jonah Hill) tries to impress the now-widowed Valka (Cate Blanchett), a Dragon Rider earlier revealed to be Hiccup’s mother, while birdbrained twins Ruffnut (Kristen Wiig) and Tuffnut (Justin Rupple) inadvertently jeopardize everyone’s safety. Outed as gay in the previous film, Gobber (Craig Ferguson) is otherwise treated no differently from any other member of the Berk community, which ultimately feels far more progressive than making a fuss over his sexuality — and which, like handicapping Hiccup with a prosthetic leg, is yet another of the ways this franchise defies the “rules” of family animation.

On the bad-guy side, Grimmel represents an improvement over megalomaniacal warlord Drago Bludvist, although it’s a shame that these sequels feel obliged to supply single-minded antagonists (this one armed with a too-convenient serum for brainwashing dragons) when one of the things that made the original so great was the way it dealt with its characters’ conflicting philosophies and the very real challenge of overhauling a society’s entire way of thinking. To some extent, Grimmel — whose chilly Gallic-inflected vocal performance puts him on par with some of the great Disney villains — represents an extension of the more primitive beliefs that Hiccup’s father, Stoick (Gerard Butler, heard in flashback), once held about dragons. As any watcher of contemporary world politics can attest, progress made can always be undone as the pendulum swings back, and Grimmel might have been a more intimidating adversary if some of Hiccup’s followers had been swayed by his vaguely Hitler-like hate speech.

However, even without Grimmel around to force an exodus from Berk to a place called Caldera — the “hidden world” of the film’s title, a visionary habitat for more dragons than you could possibly count — the film could have spun ample intrigue, what with the Light Fury’s arrival presenting an alternative fate for Toothless. Apart from tiny round Hobgobblers, beachball-size fang-monsters who multiply like Tribbles, the series has never really addressed the issue of dragon breeding. And now it must, since the white dragon — in addition to teaching Toothless cloaking and a few other new tricks — poses an inevitable dilemma, as dramatized in films such as “Born Free,” where human-animal bonds are tested by the call of the wild.

This is where “Hidden World” soars, set to the ecstatic strings and Gaelic ululations of John Powell’s score, as the mating ritual — from a delightfully clumsy courtship dance to a high-flying sequence that might later be considered the two dragons’ official first date — lends itself to long passages with little or no dialogue. From its inception, this series has insisted on a widescreen style different from that of other animated features, attempting to map the live-action idea of “magic hour” onto virtual landscapes and stylized human figures. Here, the visuals outdo anything we’ve seen before, to such a degree that we might almost overlook the subtler innovations in the character animation: the nuances of expression on both the human and reptilian faces, and the wonderful nonverbal tactics the artists use to convey emotional intricacies neither Hiccup nor Toothless has had to communicate before, all of which pays off in an unforgettable final scene.

This is uncharted territory for animated movies. No matter how Pixar spins it — about waiting until the right idea comes along to continue the story — from “Finding Dory” to last year’s “The Incredibles 2,” toon sequels have always been driven by financial considerations. Granted, “Dragons 3” (as DWA staffers refer to the film internally) was hardly made for charitable reasons, but there’s an integrity to DeBlois’ approach that won’t be lost on audiences, who probably don’t know or care that the project survived massive changeover within the studio, including Jeffrey Katzenberg’s departure and the acquisition by NBCUniversal, while holding true to the principles with which it was conceived — namely, to wrap the story in a sincere and satisfying way. We’ll soon see whether “Toy Story 4” can say the same.