Since it ended in 2019, there has been surprisingly little scholarship or nostalgia about The Big Bang Theory -- with one big exception: looking back at the series' original, unaired pilot provides an insight into the show's future, what worked, and what didn't in a more dramatic way than almost any modern example. Much of it started with the woman at the center of the show's story, Penny. Or, as she was called in the original pilot, Katie. Originally played by Amanda Walsh (Sons and Daughters), Katie's character description in the unaired pilot script had her pegged as "a street-hardened, tough-as-nails woman with a vulnerable interior."
It's difficult to imagine anyone describing Penny as played by Kaley Cuoco as "hardened," and that was the key to the changes that made her character work for audiences. While fans and critics were often divided on the virtues of The Big Bang Theory, those who first saw that original pilot were unanimous: it was passed on by every network it was shopped to, including CBS, where it would eventually run for a decade.
"I had actually auditioned for the original pilot, and I did not get cast," Cuoco revealed in bonus features on the Complete Series box set released in 2019, describing Katie as "a dark , brooking unhappy woman."
"[It] was just a mess. Not because of the actors, but because we didn't really understand the characters yet," series creator Chuck Lorre said in the same featurette. "We had to go through that failure to understand that if a woman was going to be in [Leonard and Sheldon's] ecosystem, she had to be gentle with them because they were really vulnerable."
Katie is the most famous change, but it's worth noting that there were a significant number of key changes that had to be made to the series in order for it to become the pop culture phenomenon it was. The original vision for the series had no Howard and Raj, but rather a woman named Gilda (Iris Bahr). While she later became the template for the character of Amy, the pilot's version of Gilda played much differently, too. She was already a presence in Leonard and Sheldon's lives, and quite a territorial one, at that. That version of the series would have created a "love rectangle" between Leonard, Sheldon, Gilda, and Katie.
And oh, yeah -- Sheldon was a bit of a horndog in the original pilot, which made him seem less lovably awkward and more like an incel. It would have fundamentally changed the way his character engaged with everyone, but particularly with women -- and he may have ended up competing with Leonard for either or both of the girls' attention.
For a fuller breakdown of how the original pilot failed to land, complete with clips from the show itself, you can check out this video from Nerdstalgic:
The character of Katie has been described as "cold" in virtually every look at the pilot, and while that phrase is often used to dismiss characters who are women if they don't conform to comfortable sitcom boxes, there doesn't seem to be such a sweeping generalization going on with Big Bang. Katie was mean and manipulative, and while the boys weren't quite as likable as their final form would be, that wasn't quite enough to make audiences forgive how she seemed to be taking advantage of their good nature. Her relationship with Gilda also started off on an odd, hostile note, as Gilda essentially challenged her to be the "dominant female" in the friend group, and Katie responded by flashing her, suggesting that she could use her sexuality to control the boys if she wanted to, but it would "never happen" since she wasn't interested in them.
Happening in full view of the guys, this made for an odd, awkward scene, and laid bare Gilda's intentions ("coupling" and "offspring" come up in that first scene) in a way that would have made her relationship with the pair fundamentally different to what eventually came from Amy. It's hard to imagine putting the toothpaste back in the tube, and offering a character whose motivations had any kind of ambiguity; one almost imagines someone like Sam Malone from Cheers, who declared his physical interest in Diane from the first episode. Their relationship was then defined by that.
Thankfully for fans of The Big Bang Theory, anyone who doesn't actively seek out a bootleg on YouTube was spared that take on their favorite characters.
"Chuck called a year later and said, 'It's a new character, we want you to come in," Cuoco recalls. "I read for it and it just felt so much better than it did the year before. I guess it was just meant to be."