In October 2008, DreamWorks Animation CEO Jeffrey Katzenberg handed Dean DeBlois and Chris Sanders the task of giving new life to a moribund feature-length animated film project that had been in the works for nearly four years. If that weren't challenge enough, the co-directors had to reinvent How to Train your Dragon in less than 15 months — a task that usually takes three years.

There was more at stake than simply taking the reins from previous director Peter Hastings (The Country Bears), who left the project when his wife passed away. In addition to the reported $165 million budget, the film represented a major shift for DreamWorks Animation, which had a stellar record with a green ogre (Shrek), a zoo full of animals (Madagascar) and a bamboo-eating bear (Kung Fu Panda), but hadn’t fully delivered on the human front.

“Disney had done that,” says producer Bonnie Arnold. “This was a little different for us. Here was a kid protagonist at the time when Jeffrey was trying to create an identity for the studio.”

But the early version of Dragon wasn’t shaping up to be anything that DreamWorks might want to hang its hat on. “We realized we needed something that would take us beyond the book,” says Arnold. Indeed, the source material, British children’s author Cressida Cowell’s 2003 book series of the same name, may have conjured up a wildly imaginative mythical world of Vikings who cohabitate with dragons, but it is also a very small story about a 10-year-old boy and his pet dragon.

Sanders, the 50-year-old director suggested by Arnold as Hasting's replacement, was immediately interested in taking on the task. (Sanders and Arnold had worked together at Disney on such films as Tarzan and Toy Story.) He brought his Lilo & Stich co-director, DeBlois, on board and together they met with Katzenberg, who, in addition to declaring the rock-solid release date of March 26, 2010, also assigned his new directors three tasks: They had to hang the story on a father-and-son relationship; have the smallest Viking take on the “biggest, baddest” dragon; and also set a broad tone for the film that could rival the biggest family films (e.g.: Harry Potter).

Sanders and DeBlois, 40, took two weeks reviewing the work that had already been done, and came up with a new take. First, they wanted to “age up” the lead kids in the story to early teens. They also wanted to replace the book’s cowboys-and-horses dynamic between the Vikings and dragons with one that was war-like and perilous. And, last, they wanted to make Hiccup’s pet dragon, Toothless, who was a cute iguana-sized runt in the book, into a giant, fierce creature whom he’d have to befriend, and then fly (in Cowell’s series, Hiccup doesn't get a ride until the sixth book).

Katzenberg liked what he heard, and encouraged the directors to “put the pedal to the medal,” according to Arnold.

“We knew we didn’t have time to explore,” Sanders says. “We had to get this right the first time.”

They could build on the work already done on the diverse population of dragons as well as keep the animated sets of the Viking village of Berk and its environs. The voice cast was also almost entirely set, with Jay Baruchel as the voice of Hiccup, America Ferrera as tough Viking chick Ingrid, and Gerard Butler in the role of Hiccup’s father, Stoick. But the directors had to dump most of their recorded dialogue, because the screenplay had to be entirely rewritten. DeBlois says that nothing of the earlier drafts survived.

Surrounded by bulletin boards filled with storyboard scenes, DeBlois and Sanders hunkered down to write, sitting across from each other in their office on the main floor of DreamWorks Animation’s Glendale campus.

Although they were under the gun, DeBlois reports that the production mood was optimistic. “I’ve worked on a lot of stinkers,” he says. “There’s the term, ‘polishing a turd,’ where you know that the movie’s not going to be very good but you work on weekends anyway. In this case, everybody felt confident.”

One of the key scenes they focused on early was dubbed “forbidden friendship,” in which Hiccup and Toothless cross a threshold of trust. The outline of the scene was that the dragon is injured and the young Viking brings him food. They knew that the scene would be musically driven “and pretty,” DeBlois says, “but how do they make that connection?”

Sanders came up with the idea that Toothless would begin to mimic Hiccup’s gestures, like his smile, which would create the bridge toward their budding friendship. Inspired by the image of the encounter, Sanders illustrated the scene before writing it.

The directors used The Black Stallion as inspiration as they recreated Toothless. They thought of him as a giant pet — part horse, dog and cat. And they worked in a damaged tail, which would bring Hiccup closer to him, when the boy creates a prosthetic that has a “Miyazaki vibe to it,” says DeBlois, referring to the Japanese animation master.

As the writing progressed, scenes were pushed down the pipeline: Storyboards were generated, layouts were constructed and previsualizations created rough mock-ups of the scenes in motion. (Scenes that were flagged to be particularly conducive to 3D treatment were then developed by a dedicated 3D department.)

DeBlois and Sanders also went back and forth to record dialogue sessions with their cast, most of whom did about 10 two-hour recording sessions over the space of three years, while Baruchel did closer to two dozen. The 28-year-old actor says the change of directors had been, at first, “nerve racking,” but he was quickly won over by DeBlois and Sanders’ “massive vision.”

With the new directors, Baruchel had to “age up” his character’s voice, which remained very un-Vikinglike in contrast to the two elder leads, played by Scotsmen Butler and Craig Ferguson, who plays Gobber, an advisor to both father and son. “It was this great audible way of hammering home the generation gap,” Baruchel says. “Those guys have this brogue and the rest of the kids are, like, from the mall in Sherman Oaks.”

Ferrera says that the process of voice acting could be mind numbing. “When you say the same lines 25 different ways, the words don’t sound like English any more,” says the actress, whose character, originally a marginal one, became Hiccup’s love interest as the script developed.

At the same time, other teams of filmmakers were at work. Sound designer Randy Thom was putting in nine-hour days at the Skywalker Ranch in Northern California; one of his primary tasks was to create sounds for the dragons. “One of the earliest conversations we had was not to have dragons simply opening their mouths, fire coming out and then them closing their mouths,” Thom says. “We wanted to make their bodies and cheeks vibrate.”

Thom manipulated the sounds of horses, whales, elephants and even his own low voice to create Toothless’ unique utterations; blending the different sources could be a challenge, and Thom used certain tricks — such as having the mythical creature take a deep breath between vocalizations from different sources — to achieve the desired effect.

Equally tuned in to the sounds of Dragon was composer John Powell, who was entrusted to provide the film's score. Powell immersed himself in the images and drawings being created by the art department, and listened to Finnish composer Jean Sibelius for inspiration. But, ultimately, he steered away from authentic Nordic influences and toward Celtic melodies. “We fudged the lines a little bit,” says Powell, who wanted to complement the Scottish brogue of the cast elders.

An unlikely addition to the Dragon team was Roger Deakins, the revered cinematographer best known for working with Joel and Ethan Coen on such films as No Country for Old Men — a far cry from the world of animation. DeBlois and Sanders had asked Deakins to come in to talk about his “theories of light” in a couple of workshops, in the hopes that the Dragon animators could integrate more dramatic realism in their work.

When Deakins and the animators clicked, DeBlois and Sanders decided to hire him as a full-time consultant, which helped create a unique look for the film, one that can be seen from the start, in the shadowy opening scene when the dragons invade Berk at night, with parts of the frame falling into total darkness. “Most of the time, when you see an animated film, an artist has created an original piece of art and then they just match the light to the painting,” Sanders says. “So you get an illustrative vibe. In this movie, we lit it like you’d light a live action set. We moved the lights. And that was Roger.”

The team effort behind Dragon included changes from the top as well. Despite Katzenberg’s mandate to make the release date, he threw the production’s biggest curve ball about six months before the film’s release. After an update from the directors, Katzenberg told them that the conclusion of the third act needed to be changed.

“‘You really have to do something different,’ ” Sanders recalls him saying of the way Hiccup defeats the giant, evil dragon. “It felt pat with Hiccup defeating the goliath and everything being fine in the end.”

And so, again, DeBlois and Sanders went to their office to come up with a proposal. They considered killing off a character. And then they recalled an idea that had been batted around earlier, about Hiccup getting hurt in a way that mirrors Toothless’ broken tail. They decided to have him wake up after the final battle, alone, without a leg. Arnold acknowledges that there were concerns that kids in the audience might be disturbed, but test screenings eventually allayed those fears.

Katzenberg wasn’t the only DreamWorks titan to put his fingerprint on Dragon. The directors were well into production on that third act when principal partner Steven Spielberg sat in on a special Glendale campus screening. When the lights came up, he hung around to speak with the directors.

“He gave us one of the key notes,” DeBlois says. “He mentioned that because this relationship between Hiccup and Toothless begins in a private place, that it should conclude in the same way. We had never thought about it that way.” Spielberg’s suggestion was that Hiccup should wake up with a prosthetic, but with Toothless there by his side.

It was a significant addition, but even that was overshadowed by the benediction Spielberg delivered as he walked out of the theater. “He said, ‘I love that you didn’t make any compromises,’” recalls DeBlois. “‘This is the best piece of work we’ve done at this company.’”