Prior to Kaley Cuoco, actress Amanda Walsh was cast to play Katie, “a street-hardened tough-as-nails woman with a vulnerable interior.”

"We did the very clichéd, in the beginning, goofy blonde who says foolish things," Lorre says of the character Penny.

"The Big Bang Theory" co-creator Chuck Lorre says Kaley Cuoco's character Penny took a few seasons to fully understand. "It's a cliched character: the dumb blonde, and we missed it," Lorre said during the first episode of "The Official Big Bang Theory Podcast.