Dean DeBlois and Chris Sanders are the writer-directors behind one of the best family films of the year, “How to Train Your Dragon.” It was a very great pleasure to talk with them about adapting the popular books and the movies they love most.

One of the great pleasures of this film is the fabulously imaginative assortment of dragons. Were they based on research into legends about dragons or did you start from scratch?

DD: The well-spring of the dragons who are in the film started in the book, of course, but really it was Nico Marlet, who also did designs for Kung Fu Panda. We have seven dragons in the movie, five of which are his designs. He has piles of drawings in his room, no kidding, about two feet thick of other dragons that he drew. It’s endless. We realized we had an opportunity in this movie to do something that had not been done before — not just multiple breeds of dragons but individual personalities.

Each new dragon turned all my thoughts on what a dragon was upside down.

DD: Each of them was based on animals we recognize in the animal kingdom. For example the gronkles, the big, fat, dump-truck-like dragon, was based on the walrus and has walrus-type behavior, lying around in packs and being lazy and grumpy. And then the nadders, the blue ones with the yellow spikes, they’re very parrot-like, and they have bird-like actions. Toothless is very feline. But he has dog in him, too. He’s based in part on the black panther, so he has mammalian qualities to him. One of the characters has two heads and is very snake-like and slithery. So every one of them had an animal reference to it, and that influenced its behavior both in personality and movement.

Did you have to think about the physics of the way they moved?

CS: There are links to the larger world that we wanted to create for this film. The believability factor was the most important thing. They have to move and breathe as if they’re really alive. It’s important that they not come across as too cartoony because then we would lose the emotional weight in the film. We wanted people to really believe in this world. Even though the designs are really fanciful, they move and breathe as though they’re really alive. They adhere to a strict set of rules. They never break or shatter that illusion.

The voice talent is terrific. But your Vikings (Gerard Butler and Craig Ferguson) have Scottish accents!

DD: It’s a conceit. It’s silly and admittedly flawed, but here it is: growing up in North America, I was in Canada, I had a lot of friends whose parents sounded like they came from somewhere else. There’s always a remnant of the mother tongue in the older generation. When we came on the film, they’d already cast people with very American voices and then they had Gerard Butler. We had to cast someone to be Gerard’s best friend and the confidante to Hiccup. We thought, we’ve already got this Scottish voice in place, and we could just flesh out the rest of the older generation with Scottish accents and then the next generation could have their own assimilated accent.

CS: Gerard really loved it when we encouraged him to be himself. The only casting that we did was Craig Ferguson and he happens to be Gerard’s really good friend and they happen to have the same accent. Craig Ferguson is completely at ease in front of a microphone. It’s funny because Gerard Butler is really funny off-mic, constantly goofing around and talking about pranks, amusing himself. And then when he’s on mic, well, his character is called Stoick. He was a little jealous — “Why is Craig getting all the funny lines?” But Craig, off-mic, was the opposite. He’s so funny when you have the mic running, and then when you stop, he’s actually a serious guy.

I was also thrilled to see that you have three disabled characters. You rarely see that in movies, especially disabled characters who have full personalities and experiences and are not just there to be disabled.

DD: Definitely we brought to the mix the ending, for many reasons. We wanted to give it a little bit of weight, believability, and peril. The satisfying quality of the ending would be generic if he did not come out of it so that he and Toothless can complete each other.

How did you go about adapting the book? You made some big changes.

CS: The main reason Dean and I were asked to come into the film was to “age it up,” giving it a little more weight, more adventure, and one of the very first decisions we made was that in the book there were elements of humans and dragons being in a symbiotic relationship but also elements of humans and dragons being at war. We decided it had to be one or the other. We made the decision that they were mortal enemies, which made it possible for Hiccup to take the greatest risk possible by befriending one. It allowed us to have Hiccup live this double life in the second act. At night he’s repairing a dragon and learning to ride a dragon. By day he is learning to fight one. This is not going to last. This has to get discovered. Everything else came from that.

DD: It’s fun that by the end he gets everything he wanted but he no longer wants it. The attention he’d rather avoid by then.

What movies are your favorites?

CS: Both of us are huge fans of a movie we referenced in this one, The Black Stallion. The scene on the beach is our homage.

DD: What really worked for us was the young protagonist. I love characters that are young and relatable in their childhood but also have adult qualities and are in over their heads in a world of fantasy, like “Escape from Witch Mountain,” “Watcher in the Woods,” and even “E.T.”

The movie is very rich, very exciting, but also exceptionally well-paced and satisfying.

CS: A lot of movies do not have much in the second act, but we really had one packed with events. But it is also important to have moments when the characters are quiet. There are three moments in the film where we let the camera and the acting and the music tell the story.

I liked the fact that he is really an engineer, a problem-solver. And he doesn’t get it right away.

DD: In the concept of the book Hiccup was much younger and they collect eggs and teach the dragons to do tricks. We kept the spirit of the runt Viking who changes the world but we had to give him a dragon who could be ferocious and at the same time cuddly. We thought he’s a nuisance, he’s the bane of the Viking community. He is made an apprentice to get him out of the way but in the shop he learns to compensate for what he doesn’t have. We combined this organic form with early mechanics.

CS: He also discovers that he has to operate it. He is only really himself when they’re together.