5. Heart & Soul

Docter’s first plan for Carl was much more poignant than the final version he settled upon.

“At first, Carl just wanted to join his late wife up in the sky," Docter says. "It was almost a kind of strange suicide mission or something. And obviously that's a problem. Once he gets airborne, then what? So we had to have some big goal for him to achieve."

Eventually, Docter and Peterson weaved a story that follows Carl trying to live the adventure that he and his wife Ellie always planned but never achieved.

Over time, the narrative evolved to show a quick recap of the couple’s life together – which is one of the finished film’s most affecting moments, a 4 ½ minute waltz through their relationship – before sending Carl off on his journey.

To add extra kid appeal, the writers also created Kevin, a colourful, wacky bird that lives in the Mountains, and Dug, a dog with a clever collar that lets the pooch speak whatever he’s thinking.

Later in the process, Docter hit upon the idea of including a child character, in the form of wilderness explorer Russell.

The overly excitable scout – based on hyper Pixar animator Pete Sohn – provided the creators with someone who could soften Carl’s character, while still making his life hell.

"He's not really ready for the whirlwind that a kid is - as few of us are,” Docter told Animation World.

And as for Carl’s look? That would need some cartoon tweaking…

Next: 'Toon Army