Bonnie Erickson was the creator of such esteemed Muppets as Miss Piggy, Statler and Waldorf, and Zoot from the Electric Mayhem band. Erickson's work is featured in the traveling Smithsonian exhibition Jim Henson's Fantastic World, and Smithsonian magazine interviewed her for the new issue. From Smithsonian:
Let's say you get a contract to make a character. How does your creative process work?
Well let me take the Philly Phanatic as an example. The managers approached us to design a mascot who could encourage fans to bring their families to the games. So we had to design a character who was child-friendly, who was playful and a little irreverent but not too silly. We'd heard from the Phillies that their crowd had booed the Easter bunny, so it was a challenge to come up with something that was not going to talk down to their audience. We wanted a character who had a life and a story. A lot of our characters are still performing today. We created Youppi for the Montreal Expos, and when the team moved out of Montreal Youppi was left without a home. So he was taken in by the hockey team. In my mind I've always thought of these characters as having a life, so they're free agents in many ways. When they lose a team, they go out and try to find another job.
"The Woman Behind Miss Piggy" (Smithsonian)