Best I can come up with is this interview I read with the director of the film Pete Docter:
Can you talk about your main characters, and if there were any inspirations or references for those characters?
Carl is largely inspired by our own grandparents, and a few other folks as well. There have been some people that I have met over my life who have been older, and at first blush it would seem kind of like a non sequitur that my wife and I’d be friends with them. We met this man named Mike Oznowicz who lived in Oakland, California. He was a widower in his 70s, and though he clearly had a huge gap in his life without his wife, he was incredibly full of life. He surrounded himself with young people. He’d always seen every new movie before I did, every show, every museum exhibit, was always looking for new ideas and culture. He was just incredible, and he taught me a lot about really engaging with the world. It’s people like Mike that teach you the way to live. He was like Carl at the end of the movie.
At the beginning of the film, Carl is stuck in a box of his own making. His wife Ellie showed him how amazing life is and how much it has to offer, and after she died he just withdrew and went into that box. We tried to use squares in the designs of Carl and in the house, to symbolize Carl and his approach to life. You see a lot of him in framed, small, flat, confined spaces in the beginning of the film. And as he begins to open up, you get more rounded shapes, more open air — kind of like Ellie is speaking through this other character, Russell.
Russell is the reincarnated spirit of Ellie. He’s that spirit of adventure — getting out there in the world and becoming interested in everything. He’s basically the opposite of Carl, and we designed him to pull Carl out of his shell. Carl is saddled with this kid, and in caring about him ends up re-engaging with the world in a more meaningful way. It’s mostly through Russell that that happens. We designed his basic shape to be like a spinning top, or a balloon. He’s always moving, and he’s relentless in his optimism and enthusiasm.
Dug the dog actually came from another project that Bob [Peterson, co-director / co-writer] and I developed. Those of us who have pets, we often end up making up dialog for them. Our dog will come up to my kids and stare at them, and I voice something like, “Could we go for a walk now, could we, could we, please, please?” And we thought of this unique approach to have these collars that translate what the dog is thinking, rather than have lip synced dialog. Bob wrote the dialogue for Dug and ended up voicing him – he channels dogs really well. Oh – also, Bob tells a story of being a camp counselor in High School, and this kid came up to him, gave him a big hug and said, “You are my counselor and I love you!” Dug is just a simple dog, he just wants to please people.
Muntz is a world traveler extraordinaire. He’s a combination of Howard Hughes and Charles Lindbergh, and a little bit of Walt Disney thrown in — these people who had taken these amazing risks and done things no one else had done. We looked at a lot of real life adventurers like Percy Faucett and Roy Chapman Andrews and combined them into one guy. For Carl and Ellie, Muntz represents what they want to do with their lives: “Someday, I want to be like this guy!”