'The Big Bang Theory' co-creator admits they originally missed the "brilliance to Penny's character"

In the unaired pilot, Amanda Walsh played a character named Katie, who was eventually replaced by Cuoco's role. Penny "brought a humanity" to Sheldon and Leonard, who were portrayed by Jim Parsons and Johnny Galecki, but it "took a while to figure out." 

Lorre: "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."

Roth then commented, "Not only was she 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."

Some upcoming The Official Big Bang Theory Podcast guests include director James Burrows, Kunal Nayyar, Kevin Sussman, John Ross Bowie, Sara Gilbert, Christine Baranski, Vernee Watson, Sara Rue, and many more. New episodes drop weekly on Max and all major podcast platforms.