While Penny would eventually be joined by other main female characters later in the series, the first three seasons were quite different. She was the only female character in the early seasons and was often portrayed as a ditzy blonde. Penny was the subject of many jokes that would be viewed as problematic today.
This is something Lorre said he now regrets. In the book The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series, Lorre talked about the early incarnation of Penny and her development as a character.
"One of the most underwritten characters in the show early on was Penny," he said. "It was really obvious immediately that we hadn't developed the character beyond the pretty girl next door, and Kaley was certainly capable of doing a great deal more than what was asked of her. We had to make the character more fully realized. Not just for an episode, but always. [Over time] Penny had an intelligence about people, about relationships, and about sussing out a situation and understanding the dynamics of what's going on in a room."
In the same book, Cuoco shared her disagreement over Penny's character arc. Throughout the final season Penny and Leonard struggle with the idea of having children. Then, Penny discovers she's pregnant unexpectedly in the final episode. The show's fans have mostly celebrated this storyline. However, Cuoco made it clear that she actually wanted her character to take a different path.
"I actually wished that they did not [make Penny pregnant], because I loved that message [of Penny not wanting kids] so much," Cuoco said. "It was cute how the writers did it at the end with Penny's surprise pregnancy, and all in all I'm glad, but I was actually voting for her not to [get pregnant]."
To celebrate the show's 15th anniversary, creators Bill Prady and Chuck Lorre spoke with Entertainment Weekly. The two discussed many aspects of the show's history and revealed their favorite moments in the series. This discussion also provided insight into the important role Penny played in the series.
"Jim Parsons' speech about why he sits in that particular spot on the couch in the pilot episode," Lorre said when asked his favorite moment. "I think we all watched that and understood something remarkable was happening. There were no real jokes in the speech, it was just a worldview that was so precise, and he brought it to life. It was an astounding moment I'll never forget."
"I love the episode where Sheldon doesn't like that Leonard is dating Raj's sister," Prady said. "She was a lawyer and kept finding loopholes in the roommate agreement and was using it against him. Sheldon gets so mad that he ends up threatening to tell her parents she was dating Leonard and uses the Star Trek self-destruct sequence to do it."
He continued, "To me, that was this great nerd explosion. Then there's the incredible moment with the Christmas gift where Penny gives Sheldon a napkin with Leonard Nimoy's DNA on it."
Lorre added, "That's when he hugged Penny. It was the first time he laid a hand on her. That was a big character breakthrough moment, he was so alienated up to that point."
The character of Raj had many memorable qualities. One of the most memorable of the bunch was his inability to talk to women. This made for some great comedic moments in the show.
In their Entertainment Weekly interview, Lorre and Brady discussed the development of Raj's character and what the inspiration was.
"Bill worked with a guy in the 1980s, a computer programmer, that was actually like that," Lorre said.
"Yes, and that attribute actually belonged to the fellow who had most of Sheldon's attributes as well," Prady added. "Somehow, in our discussions, that moved out of the Sheldon character and into Raj."
"Yeah, we created two characters out of that one guy," Lorre said.
Prady described how he noticed his former co-worker's issue.
"It was a really interesting thing to watch because if we were talking and a woman came into the room, he would just stop talking," he said. "And then she would leave, and he would start talking again. Obviously, we started noticing it. It's a real thing, selective mutism. It's an anxiety condition. He was just so anxious around women that his solution was to not talk."
"And Penny is the one who cured Raj," Lorre added, once again noting the significance of the character. "She was the pivot point for all these characters. She was also the one who told Howard, "You're not a ladies' man… you're disgusting." But she also introduced him to Bernadette. She impacted all these characters in such a major way."
