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

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

Lorre explained that it took the show a while to understand that the character was more than a "dumb blonde" The Big Bang Theory creator Chuck Lorre is looking back on the evolution of Kaley Cuoco’s character in the beloved sitcom’s early days.