Figuring out Kaley Cuoco‘s bubbly character Penny may have been more difficult than quantum physics for the guys behind The Big Bang Theory.

Co-creator Chuck Lorre and former Warner Bros. Television Group chairman Peter Roth took time out this week to look back on the original, unaired pilot of the hit sitcom while appearing on the debut episode of Jessica Radloff’s The Official Big Bang Theory podcast.

Reflecting on how Cuoco reshaped Penny, the two admitted that the beloved character, an aspiring actress who moves into the apartment across the hall from Sheldon (Jim Parsons) and Leonard (Johnny Galecki), was initially “one-dimensional” and a cliché.

“We had so many episodes to go before we started to understand that there was a brilliance to Penny’s character that we had not explored,” Lorre said. “We did the very clichéd — in the beginning — goofy blonde who says foolish things. It was a clichéd character, the dumb blonde. We missed it. We didn’t have that right away — that what she brought to this story, to these other characters, was an intelligence that they didn’t have. A kind of intelligence that was alien to them. You know, intelligence about people and relationships and family.”

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Penny “brought a humanity” to Parsons and Galecki’s socially awkward scientists “that they were lacking,” Lorre added. “And that took a while to figure out. In the beginning, she was sadly one-dimensional in too many ways.” Lorre went on to explain that the upside of having a TV series that begins to see success is “you get time to learn” how to bring more depth to the characters.

The unaired pilot featured another actress, Amanda Walsh, as a character named Katie, before she was replaced with Cuoco and reworked to become Penny.

Lorre and Roth agreed that Cuoco brought a much-needed softness to the character, who was a contrast to Parsons and Galecki’s leads. “They could be as obnoxious — or for Sheldon, as off-putting — as possible, but you forgave them, because there was this kind of childish naiveté,” Lorre said of the two roommates. “The magic of Kaley was, Kaley’s character — as we figured this thing out on the fly — was amused by them, not critical. If she got angry, it wasn’t harsh. The audience really responded to that.”

Added Roth, “Not only was she was never judgmental about these characters, they brought more judgment to her than she did ever of them. And I thought that was also an important difference between the character of what Penny brought versus the character of what Katie brought in the original, unaired pilot. There was a sweetness and endearment that she felt towards them. I think the audience wanted to protect these two boys, these two men, these two innocents. And she honored that.”

The Emmy-winning sitcom, which ran for 12 seasons between 2007 and 2019, centered on Cuoco’s Penny, a waitress and an aspiring actress, as she moves into a Pasadena apartment across the hall from the socially inept but super-smart scientists Sheldon and Leonard. Throughout the course of the series, she shows them just how little they know about life outside the lab, and becomes Leonard’s love interest and, eventually, his wife.

Listen to Lorre and Roth’s full podcast discussion above.