A draconian test: the muggles at ILM conjure up a digital dragon in the latest Harry Potter feature The Goblet of Fire.(Industrial Light & Magic)

In Warner Bros.' Harry Potter and the Goblet of Fire, the young wizard's nemesis is a fire-breathing dragon with a spiky tail that can slap the teenager around, claws on its wings so it can walk, and the ability to fly as fast as Harry on his broomstick. It's a "horntail" dragon, the most dangerous kind, and it stars in 145 shots, all created by Industrial Light & Magic, one of seven facilities that added digital wizardry to Harry Potter's latest adventure.

"It was our main sequence," says Tim Alexander, ILM visual effects supervisor. In addition, the studio created a hero shot of a magical boat (see "Out of Water," pg. 40), the world-cup Quidditch match and stadium in the beginning of the film, and a few other one-off shots.

The dragon sequence begins in an open-air arena built inside a rock quarry. There, a large golden egg glows atop a boulder guarded by a fiery dragon tethered to a long chain. To win the Triwizards Tournament, Harry must retrieve the egg and find a clue for the next task. He enters the quarry timidly, and hides behind a rock. When he scampers toward the egg, the writhing dragon attacks with its spiky tail. The young wizard calls for his broom and flies out of the dragon's reach. But, the dragon breaks free and gives chase. Harry heads for Hogwarts with the dragon blowing fire at his feet, and the action sequence takes off.

To build the CG dragon, ILM scanned a half-scale, 30-foot-long maquette with a 14-foot wingspan. Plates covered the dragon's long tail. Little claws hung from its wings like tiny hands. Modelers at ILM then sculpted the CG creature using one Alias Maya unit to represent one foot in real space. They relied on displacement to create wrinkles on the leathery skin and wings and to create the small plates, but modeled the tail's bigger scales.

The modelers also created shapes that the animators could dial in and out to emulate the creature's moving musculature. "We talked about doing flesh sims, but it was better to put the controls into the animators' hands," Alexander says. ILM's cloth-simulation engine, however, animated the wings. To decide how thick to make the bat-like wings, character-look developers showed Jimmy Mitchell, the film's overall visual effects supervisor, various simulations that used combinations of flexibility and springiness until he found a setting that he liked.

Bird of Prey

While the creature-development team modeled, textured, and rigged the dragon, animation director Steve Rawlins sorted through reference material, working with Mitchell to shape the dragon's attitude.