The Big Bang Theory's Co-Creator Bill Prady Explains How Leonard And Penny Almost Didn't End Up Together

"The Big Bang Theory" — the popular CBS sitcom created by Chuck Lorre and Bill Prady, that ran from 2007 to 2019 — follows the lives of a group of scientist friends and one aspiring actress. There are roommates Sheldon Cooper (Jim Parsons) and Leonard Hofstadter (Johnny Galecki), two theoretical physicists with high IQs, as well as aerospace engineer Howard Wolowitz (Simon Helberg) and astrophysicist Rajesh Koothrappali (Kunal Nayyar). Rounding out the original group is Penny (Kaley Cuoco), an aspiring actress who lives across the hall from Sheldon and Leonard. Later on, the friend group expands to include Bernadette (Melissa Rauch), a microbiologist and Howard's eventual wife, and Amy (Mayim Bialik), a neurobiologist and Sheldon's love interest.

Throughout the show's 12 Seasons, a major story thread was the on-again-off-again romance between Leonard and Penny. After meeting in the pilot episode, Leonard is instantly attracted to Penny, but it takes until Season 3 for the pair to finally start dating. After more ups and downs, the couple finally gets engaged in Season 7. In the series finale, we find out that Penny is pregnant with their first child.

It's a happy ending, indeed, one that fans were likely expecting ever since the two of them were set up as a will-they-won't-they couple in Season 1. However, Penny and Leonard ending up together wasn't always in the cards, surprisingly.

In Jessica Radloff's book, "The Big Bang Theory: The Definitive Inside Story of The Epic Hit Series," which was published in October of 2022, co-creator Bill Prady opened up about writing the Leonard-Penny romance. And he dropped one pretty major bombshell: It was never a sure thing that Leonard and Penny would end up together.

Prady explained, "After an exhausting first season, we came back in June and started up the writers' room; just having conversations about where the season could go. I think one of the things that I ultimately came to embrace about Leonard and Penny as a couple is that they had a rough go of it, they broke up and got back together, and there were periods where they saw other people" (via Google Books). He explained that they saw Penny and Leonard's relationship as different from other iconic TV couples, such as Ross and Rachel from "Friends," in that he and the other writers didn't view them as having an inevitable happy ending as a couple.

Instead, they wanted the relationship between Penny and Leonard to play out naturally. Prady continued, "We said they legitimately could be the person for each other and we were rooting for it, but they had a lot of obstacles. So when they'd break up, it wasn't false jeopardy for the audience. Them not winding up together was an absolute legitimate path forward for the series, and it could've been. They could have easily been that couple who once went out and now are friends."

As ardent fans of "The Big Bang Theory" already know, Kaley Cuoco and Johnny Galecki, who played Penny and Leonard, also dated for a couple of years off-screen. Their real-life romance was also chronicled in Radloff's book about the series. But the actors' relationship may have been more than just an interesting tidbit for fans. Cuoco thinks that their off-screen relationship helped make the Penny and Leonard pairing so appealing.

In Radloff's book, Cuoco stated, "I think a lot of what made Leonard and Penny work so well was my relationship with Johnny off camera, which turned into such sarcastic banter that bled into Penny and Leonard. Johnny and I's relationship, in a way, was mimicking Penny and Leonard. They were always giving each other s***, and Johnny and I have a similar relationship — which you do after years of being together" (via Vanity Fair).

The actress then went on to describe how she and Galecki continued to have a friendship after they broke up — which, as fans know, mirrors that of Penny and Leonard, who still continued hanging out together even when they were not actively dating. Cuoco said, "We've always had each other's backs, and you can't lose that. And I do think it happened on-screen. It made our relationship funny and endearing."