"The Big Bang Theory" is easily among the most popular sitcoms of the last couple of decades. Alternating between lovingly embracing and outwardly mocking nerd culture, the series ran for 12 seasons on CBS and racked up before wrapping up in the spring of 2019. However, all of that could have been erased if the show's pilot fell face first.

While Sheldon Cooper (Jim Parsons) would go on to become the fan favorite on "The Big Bang Theory," his chemistry with fellow lead Leonard (Johnny Galecki) wasn't originally enough to get the show a pass for its first season.

The initial pilot for the series actually contained two other characters that were inevitably cut out. Katie (Amanda Walsh) and Gilda (Iris Bahr) were in the first draft of the series premiere but were ultimately replaced by another actor.

Penny (Kaley Cuoco) turned out to be the missing ingredient that the series needed to make it past the cutting room floor. "There was so much about the pilot that did work," former CBS Entertainment chairwoman Nina Tassler told Emmy Magazine (via ). "But there were parts of the script that didn't work, and we had to recast an actress. [Chuck Lorre] is such an extraordinary talent.

He had a great concept and wonderful chemistry between the two leads, so I asked him if he would try again." 

Knock, knock, knock, Penny is just what the show needed

This request is how the character of Penny ended up coming to be on The creator of the series, Chuck Lorre, and producer Bill Prady were able to restructure the pilot in a way that made it work for the executives at CBS. "[Lorre] immediately said, to his credit, 'You're right, I know I can do better. Thank you for this opportunity, and we'll figure it out.

' Sure enough, he did," Nina Tassler explained. "Kaley Cuoco joined the cast, and she was the secret sauce. Chuck and Bill Prady delivered a pilot script, and the rest is history."

Still, it was Penny's kindness that helped to make the difference for test audiences, and the reasoning for this is a bit surprising. Despite their intellect being a key part of "The Big Bang Theory," initial viewers felt somewhat protective of Leonard and Sheldon. "That's why we rewrote Katie to become Penny [Kaley Cuoco] and made her much more charmed by the guys and kind to them, as opposed to a woman who would take advantage of them," Lorre explained.

It looks like the choice to scrap Katie and Gilda in favor of Penny turned out to be the right move for "The Big Bang Theory," and the character ended up staying on for the entirety of the series as a result. Luckily, though, she did eventually get a bit of reinforcement in the form of Bernadette () and Amy (Mayim Bialik).