Elizabeth Blair of NPR has interviewed many people, but she may have just met her match in Cookie Monster. From a February 2009 All Things Considered interview:
Years before Sesame Street, Muppet creator Jim Henson made a very similar monster who ate snack foods and computers in television commercials. The basic look and spirit were there, but the character we know today was still a ways off.
Enter puppeteer Frank Oz. For nearly 30 years, Henson and Oz were an extraordinary team. Cheryl Henson, Jim's daughter and the president of the Jim Henson Foundation, says the two men shared a subversive sense of humor. Their Muppets were regulars on The Ed Sullivan Show and The Tonight Show.
It was later, on a Muppet game show, that the cookie-fixated creature we know emerged, Oz says. The winning contestant was offered the chance to choose a prize: a vacation, a new house, $10,000 cash, or a cookie. He chose the cookie — and the Cookie Monster was born.