Indeed, Lasseter's demand to keep the toys faithful to the film characters led him to reject prototypes with even slight deviations, as was the case with a Wall-E toy that rolled on wheels.
"John rejected the hidden wheels design and preferred that Wall-E's treads be real working treads just like the character in the movie," Thinkway Toys Chief Executive Albert Chan said in an e-mail from Hong Kong. "It was important to him to keep the character's integrity in the toys."
Lasseter said his visit to El Segundo, where all the Disney Princess regalia was on display, helped shape his thinking about Princess Tiana.
He said he came to understand that each princess has items that are hers alone -- and a distinctive color, so Tiana's accouterments could be easily distinguished from Snow White's.
Tiana's look would reflect her transformation. "From the bayou wedding dress, Princess Tiana became identified with the color light green -- reflecting the lily pads and the frogs," Lasseter said. "That was unique to her."
Once Mattel had refined its ideas for the toy line, Lasseter and the filmmakers weighed in.
Mattel's design team focused on capturing key story elements that children would want to re-create, such as Tiana changing into a frog.
Lasseter believed the toy company had overlooked the possibilities for minor characters Louis the jazz-playing alligator and Ray the Cajun firefly.
"My job sometimes is to point out to people which characters are going to be great -- and kind of encourage them to pay attention since the audience will love them," Lasseter said. "I pushed to get the Ray and Louis toys made."
The bug-eyed Ray seemed an unlikely object for the toy box, said Mary Beech, general manager of studio franchise development for Disney products. "When you see it in black and white at first, it's hard to say kids are going to want to play with a bucktooth firefly," she said.
But with Lasseter's cajoling, Mattel added the character to an 11-piece set.
Ask Lasseter to explain the appeal of the "Princess and the Frog" merchandise, and he points to the enduring appeal of the Disney fairy tale.
"One of the first decisions we made, when [Pixar and Disney Animation Studios President] Ed Catmull and I came to Disney was to return to the sincere fairy tale," Lasseter said. "I never quite understood why Disney hadn't made a sincere fairy tale since 'Beauty and the Beast.' My two nieces would dress up in princess outfits all of the time. I realized there was this huge audience out there for this."