'Big Bang Theory' without Kaley Cuoco? These actresses auditioned for Penny.

What would The Big Bang Theory have been like without Kaley Cuoco?

That was almost the reality. The new book, The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series by Jessica Radloff, details how actresses Marisa Tomei, Tara Reid and Elizabeth Berkley were all up for the role of what ultimately became the Penny character. And, in fact, for a hot minute, Penny, the aspiring actress turned pharmaceutical sales rep and half of the popular Penny/Leonard pairing, was "Katie."

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The Big Bang Theory without Kaley Cuoco? We look at the well-know actresses who auditioned to play the part of Penny. It was a role that evolved from its original conception — and two other actresses were actually cast prior to Cuoco making it her very own. (Photo: Cliff Lipson/CBS via Getty Images)

The history of Penny on BBT, which ran from 2007 to 2019, is an interesting one. Per a book excerpt in The Hollywood Reporter, after Jim Parsons and Johnny Galecki were cast as Sheldon and Leonard respectively, it was on to cast Penny. However, at the time, CBS had another pilot with a character named Penny, so creator Chuck Lorre was asked to change the name. It became Katie — and the role was nothing like the bubbly Nebraska native; she was older and cynical.

Cuoco, off of 8 Simple Rules, actually screen tested for the original Big Bang pilot, but didn't get it. Casting director Ken Miller said she was "so sunny and bubbly" and while they "just loved her," Katie was a darker role. Cuoco "just wasn’t the essence of Penny in that first incarnation." And at just 20, she was too young for what was envisioned.

Cuoco said, "I know Chuck really wanted me for the role of Katie, and I was definitely bummed when I didn’t get it, but I kind of have a way of moving on because you have to."

The show moved on, too. Parsons recalled that he "read with Marisa Tomei... I remember going to the snack room after we were done and telling Ken and Nikki [Valko, casting director], 'I’ve never been in someone else’s audition before!' And they said of the [Oscar-wining actress], 'Well, she was kind of really auditioning you.' And I went, 'Oh, that makes sense.” But oh my gosh what a different world that would have been" had Tomei been cast.

Show co-creator Bill Prady said, "Tara Reid also came in for the role of Katie, and I think Elizabeth Berkley went to network for the role, too. She was terrific." Canadian actress Amanda Walsh had an audition, but didn't land the role.

(Photo: Getty Images)
Elizabeth Berkley, Marisa Tomei and Tara Reid were all considered for the part. (Photo: Getty Images)

Finally, they found their Katie in actress Jodi Lyn O'Keefe (Nash Bridges, Vampire Diaries, Prison Break). They did the first table read for the pilot, then Parsons, Galecki and O'Keefe and others went out to a restaurant. By the time they all arrived, O'Keefe got word from her agent that she had been fired.

"I hadn'T done a ton of table reads in my career by that point, but I'm not an idiot — I know when someone’s not good," Parsons said. "And Jodi was great. I was stunned. But they realized during that table read that the character’s approach to the other characters was too harsh, too whatever, even though Jodi, in my opinion, nailed what they had written."

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Jodi Lyn O'Keefe was originally cast in the role that became Penny, but she was fired after the first table read. It was not personal — creator Chuck Lorre called the role "misconceived" and revamped the part. O'Keefe later appeared on the show as Mikayla, a prostitute. (Photo: Cliff Lipson/CBS via Getty Images)

The show had three days to recast and they were in such a crunch that they even held auditions on Easter Sunday. Walsh was called back to audition again and landed the recast part on the spot. She started immediately.

Prady told Entertainment Weekly in September that Katie was "kind of rough" and "dangerous in a way" in addition to being "[not] very nice to the guys," two nerdy but endearing physicists. At a test screening of the unaired pilot, "the audience hated her," Lorre said.

Lorre told that outlet, "We didn't realize early on that the audience viewed [Sheldon and Leonard] as children. They were very naïve and childlike, regardless of how intelligent they were. They were very vulnerable, and the audience didn't want a toxic presence around them." He said Walsh not working out was on them, calling the role was "misconceived."

The network asked for unlikable Katie to be recast, but the creators decide to retool the show based on feedback, adding "more of these brilliant misbegotten characters," including Howard Wolowitz (played by Simon Helberg) and Raj Koothrappali (Kunal Nayyar) who the test audience liked, and revamping Katie, making her kinder and more charmed by her geeky neighbors. Walsh wanted to come back and have another crack at playing the newer version, but they decided to recast. That's when Cuoco became Penny.

The Big Bang Theory premiered on September 24, 2007. It aired 279 episodes, received numerous awards (including Parsons's four Outstanding Lead Actor Emmys) and earned its spot in TV history.