The Big Bang Theory had one of the best ensemble casts of any sitcom, in large part thanks to the relationship between the self-professed nerds and the beautiful young neighbor who moved in across the hall. This woman, Penny, was beautifully played by Kaley Cuoco. Fans can’t imagine any other actor having captured the role in the same way. But she wasn’t originally supposed to play Penny.

There was another actor initially tapped to play a different lead female character, who was written to be quite different from how she turned out. Knowing more details about the story, The Big Bang Theory would not have worked in the same way it did, and become such a cultural phenomenon, if the original actor had been cast and Penny wasn’t part of the mix.

When The Big Bang Theory was initially proposed and filmed its first pilot, Amanda Walsh was cast as a female lead character named Katie. She was part of the show concept Chuck Lorre and Bill Prady originally pitched to CBS. But it was reportedly rejected, so they went back to the drawing board and rejigged some of the writing. This included completely changing the female lead character.

This character was still supposed to play the traditional “girl next door” role, the beautiful young woman who the geeky guys fawn over once she moves in. The idea was for her to offer a counterbalance to all the technical jargon that was core to the dialogue in the series and add a sense of realness and relatability.

Interestingly, Cuoco did initially audition for the role but was told she was too young. When she heard they were auditioning again a year later, she returned for a second shot. She got the part of a new character named Penny, and Katie became ancient history.

Of being cut from the show, Walsh told Jessica Radloff in her book The Big Bang Theory: The Definitive, Inside Story Of The Epic Hit Series, that she had waited anxiously for the phone call about the show getting picked up, and heard the no. When she later learned it was indeed being picked up after a reworking of the story, she was pleased…until she was advised that it meant she would not be part of the project.