Why Sara Gilbert's Leslie Winkle Left The Big Bang Theory

"The Big Bang Theory" played host to a ton of guest stars and supporting players throughout its 12-year and 12-season run, including a whole bunch of "Star Trek" veterans and real-life scientific experts like Stephen Hawking and Bill Nye, just to name a few. To that end, there were also a handful of actors introduced as potential love interests for the main characters, one of whom, Leslie Winkle, was played by Sara Gilbert. But who, exactly, was Leslie, and why did she (and Gilbert) leave the show after its third season?

In Jessica Radloff's book "The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series," which came out in 2022 and spilled a ton of secrets about the hit show, executive producer Steve Molaro and writer Lee Aronsohn both opened up about Leslie's short-lived time on the show, where she carried on brief relationships with both Howard Wolowitz (Simon Helberg) and Leonard Hofstadter (Johnny Galecki). As an experimental physicist who also works at the California Institute of Technology, Leslie is, for lack of a better term, basically a "girl version" of Leonard who ends up in a casual relationship with him. According to Molaro and Aronsohn, however, there was just one problem: Leonard was always supposed to end up with Penny, his dream girl played by Kaley Cuoco.

"We wanted love interests for Leonard and were just looking for stories," Molaro admitted in the book. "It was also a great way to add female scientists, because Leslie was at the university as well. And Chuck [Lorre, the show's creator] had a history with Sara from 'Roseanne' [Gilbert and Galecki both appeared on the hit 1980s sitcom]. But we were never looking for a permanent, everlasting relationship for Leonard because we always thought he would date Penny on and off. We weren't looking to find a permanent girlfriend for him. We were adding characters and seeing what worked and what was leading to fun stories."

Even though everyone involved with "The Big Bang Theory" knew that Leonard and Penny were destined to be together, the people behind the show kept bringing in new faces to test the waters — and a few of them also smartly realized that the series could get stale if it was just the original five characters forever (namely, Leonard, Howard, Penny, Kunal Nayyar's Raj Koothrappali, and Jim Parsons' iconic Sheldon Cooper). They did just this later in season 3 when they introduced Amy Farrah Fowler (Mayim Bialik) and Bernadette Rostenkowski (Melissa Rauch), but clearly, Leslie Winkle and other characters, like Sara Rue's Dr. Stephanie Barnett, were test runs, so to speak.

As executive producer and eventual showrunner Lee Aronsohn explained in Jessica Radloff's book, "We tried a couple of women in love interest roles, social-interest roles, before we came up with Amy Farrah Fowler and Bernadette Rostenkowski, and Leslie Winkle was one of them. There was also Sara Rue. We were realizing that if we wanted the show to have longevity, we had to enlarge the family." 

Still, as Steve Molaro revealed, "The Big Bang Theory" mostly flew by the seat of its proverbial pants creatively, so the show's creatives tried to remain open to any and all possibilities. "But we never planned too far ahead because we wanted things to unfold organically," he remarked. "We never arced ahead in anything, except in season 12 we were starting to plan ahead to an ending and Sheldon winning the Nobel Prize. But as far as relationships and adding characters, we really preferred to add them and see how it felt, and see how it grew naturally."

Okay, so how did Sara Gilbert end up on "The Big Bang Theory" in the first place? That one's easy. Chuck Lorre knew Sara Gilbert from her work on "Roseanne," where she played Darlene Conner — while Johnny Galecki played David Healy, Darlene's boyfriend turned husband — and simply thought Gilbert would be perfect. "When you're writing a part say, for a love interest for Leonard, and you want Leonard to perhaps be dating a scientist who is as good or better than him, and was a prickly character, you think, Hmmm, who do we know? And Sara was wonderful," Lorre explained in Jessica Radloff's book.

Later on in Radloff's book, as the creative team discussed the show's expansion that brought Mayim Bialik and Melissa Rauch's characters on board (a decision that Simon Helberg felt greatly benefitted "The Big Bang Theory"), executive producer and writer Steve Holland talked about specifically adding women in science — a description that fits both Amy Farrah Fowler and Bernadette Rostenkowski. (Amy, like Bialik, is a neuroscientist, while Bernadette gets her PhD in microbiology and starts working for a pharmaceutical company during the show's narrative.)

"There was always a desire to have more female scientist representation because it was a very male-heavy show," Holland noted. "It wasn't a thing where we were like, We're going to write this character and have her be part of the show, but it was a thought that this was important for us to do. Bill [Prady] and Chuck wanted to highlight women in science as well, but it had to be the right role. You don't just write a new character, and say, 'This is our new female scientist.' You have to find the right roles for people. Sara Gilbert kind of filled that role early on, but she wasn't part of the show as much by season 3." 

Things change, and ultimately, Gilbert just wasn't the right fit for Leonard or "The Big Bang Theory." Nevertheless, you can watch her episodes on Max, where "The Big Bang Theory" is streaming now.