"We had so many episodes to go before we started to understand that there was a brilliance to Penny's character that we had not explored," Lorre said. "We did the very clichéd — in the beginning — goofy blonde who says foolish things.

 It was a clichéd character, the dumb blonde. We missed it. We didn't have that right away — that what she brought to this story, to these other characters, was an intelligence that they didn't have. A kind of intelligence that was alien to them. You know, intelligence about people and relationships and family."

"We had so many episodes to go before we started to understand that there was a brilliance to Penny's character that we had not explored," Lorre said. "We did the very clichéd — in the beginning — goofy blonde who says foolish things. 

It was a clichéd character, the dumb blonde. We missed it. We didn't have that right away — that what she brought to this story, to these other characters, was an intelligence that they didn't have. A kind of intelligence that was alien to them. You know, intelligence about people and relationships and family."

Penny "brought a humanity" to Parsons and Galecki's socially awkward scientists "that they were lacking," Lorre added. "And that took a while to figure out. In the beginning, she was sadly one-dimensional in too many ways." Lorre went on to explain that the upside of having a TV series that begins to see success is "you get time to learn" how to bring more depth to the characters.

The unaired pilot featured another actress, Amanda Walsh, as a character named Katie, before she was replaced with Cuoco and reworked to become Penny.

Lorre and Roth agreed that Cuoco brought a much-needed softness to the character, who was a contrast to Parsons and Galecki's leads. "They could be as obnoxious — or for Sheldon, as off-putting — as possible, but you forgave them, because there was this kind of childish naiveté,” Lorre said of the two roommates.