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“The Big Bang Theory” ended in 2019, and one of the many legacies that the long-running and beloved CBS sitcom created by Chuck Lorre and Bill Prady left behind is that the series was filled with extraordinary guest stars and supporting players. Some of them, in fact, are set to star in their own spin-off. The second major “Big Bang Theory” spin-off after the success of “Young Sheldon” (which cast Iain Armitage as, well, a young version of Jim Parsons’ Sheldon Cooper from the original series), titled “Stuart Fails to Save the Universe,” will feature Kevin Sussman, Lauren Lapkus, Brian Posehn, and John Ross Bowie, all of whom played great recurring roles on the first series. 

It’s great that those actors — who played Stuart Bloom, Denise, Bert Kibbler, and Barry Kripke on the original show, respectively — are returning for more screen time. Though we don’t know if Parsons, Kaley Cuoco, Johnny Galecki, Kunal Nayyar, Simon Helberg, Melissa Rauch, or Mayim Bialik will make cameos in “Stuart Fails to Save the Universe” as Sheldon, Penny, Leonard Hofstadter, Raj Koothrappali, Howard Wolowitz, Bernadette Rostenkowski-Wolowitz, and Amy Farrah Fowler, it would actually be pretty cool if other supporting characters from “The Big Bang Theory” showed up and got to play around a bit more in this universe. The five characters listed here were highlights on “The Big Bang Theory” whenever they were on-screen, and whether they were written off or simply appeared occasionally, they just didn’t get enough play. Here are five of the best “Big Bang Theory” characters who should have gotten way more screen time.

Throughout “The Big Bang Theory,” Sheldon, Raj, Howard, and Leonard all work together as high-level scientists at the California Institute of Technology in Pasadena — and as physicists and engineers, they pretty much always need significant funding for their projects. That’s where Joshua Malina’s President Siebert comes in; as the prestigious scientific center’s president, he appears to be in charge of how funding is spread out amongst the talented scientists working there. That also explains why, when it comes to money, Siebert is pretty craven. 

At one point, he drags the guys to a fundraising event only to discover that Sheldon should never be let loose around potential donors (and also encourages Leonard to seduce a female patron, which isn’t great!). Ultimately, though, Siebert is just a peripheral presence who does stuff like “force Sheldon to finally take a vacation so Siebert can have some peace and quiet at work,” though he does recognize that Sheldon is a brilliant scientist who can help Caltech succeed.

Malina, known for “The West Wing” and “Scandal,” is always a delightful presence on-screen, and even though Siebert shows up with some regularity in “The Big Bang Theory,” it definitely would have been nice to see more of him. With his dry wit and not-so-secret disdain for Sheldon’s antics, Siebert was a great grounding presence, and he deserved some more fleshed-out plotlines.

Obviously, when it comes to Penny’s romantic endgame, Leonard is the guy for her, and after years of an on-again, off-again relationship, the two finally get married in season 9, have another wedding in season 10, and are expecting a baby together in the series finale. As far as Penny’s other boyfriends go, though, the most prominent is Zack Johnson, an affable if dim guy played by Brian Thomas Smith. Penny mostly uses Zack to make Leonard jealous, but here’s the thing about Zack — even though he’s tall, traditionally handsome and masculine, and seems like the kind of guy who would have bullied Leonard in high school, he’s actually really nice! In the fourth season of the show, the gang dresses up as the Justice League for Halloween and enlists Zack to be Superman, since he’s the only one with the correct physique; not only does Zack say yes, but he’s pretty enthusiastic about the whole thing! Again, he’s not a genius, but who cares? Zack takes a genuine interest in the guys’ “nerdy” interests and is always trying to be friendly and kind, whether or not he’s even with Penny.

Unfortunately, the writers brought Zack back late during the run of “The Big Bang Theory” for a plotline where he and his wife, who are having trouble starting a family, ask Penny to donate her eggs to them (which incenses Leonard, so Penny ends up declining). Not only is this plot weird, but it’s a disservice to Zack, a good character who deserved more play. Zack should have been a semi-regular part of the gang — he was great!

“The Big Bang Theory” brought on some phenomenal actors to play the parents of the main cast — Laurie Metcalf, Keith Carradine, and Judd Hirsch all showed up at various points as Sheldon’s mom, Penny’s dad, and Leonard’s dad, respectively — but with all due respect to those fine folks, getting Christine Baranski to play Leonard’s mom was a huge win. As the imperious and brilliant Dr. Beverly Hofstadter, Baranski brings her considerable screen presence to the character, who’s a neuroscientist and psychiatrist who, in a pretty unethical move, spent her son’s formative years mining his experiences for content. We learn that Leonard is absolutely humiliated by his constant presence in his mother’s books, and unfortunately for Leonard, Beverly doesn’t really see the problem with using her son’s actual life to sell books at first; still, even though she has a difficult relationship with her son, she enjoys Sheldon’s company and even forms a strangely close friendship with Penny.

Beverly and Leonard have a touching scene in the 12th and final season of “The Big Bang Theory” where Leonard finally explains to his mother why he’s hurt, and she tries to understand his point of view. But had that happened sooner, we could have seen Baranski and Johnny Galecki share the screen way more and perhaps forge ahead with their repaired relationship. Baranski was, I can imagine, too busy to be on “The Big Bang Theory” too often, but still: We needed more Beverly!

Leonard never dated as much as Penny did before the two settled down together, but one of his earliest love interests, Leslie Winkle, played by Sara Gilbert, was a pretty prominent supporting character in the show’s early seasons. Leslie, who also hooks up with Howard, is a bit on the manipulative side, but she’s also a brilliant scientist and shrewd woman who’s probably Leonard’s equal or, more realistically, smarter than and superior to Leonard. Unfortunately, both Leslie and Gilbert left the series after season 3 of “The Big Bang Theory,” and in Jessica Radloff’s 2022 book “The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series,” we learned why.

“We wanted love interests for Leonard and were just looking for stories,” executive producer and writer Steve Molaro told Radloff before acknowledging that it also helped to have a female scientist in the room — and noting that both Chuck Lorre and Johnny Galecki had previously worked with Gilbert on “Roseanne.” Still, as Molaro acknowledged, Leslie’s days were numbered right from the beginning. “But we were never looking for a permanent, everlasting relationship for Leonard because we always thought he would date Penny on and off,” he explained. “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.”

This makes sense, but I still can’t help but feel like Gilbert and Leslie got shafted a little bit here; just because she and Leonard aren’t dating doesn’t mean Leslie needs to vanish from CalTech entirely! When Amy Farrah Fowler joins the series at the end of season 3, she fills the void Leslie leaves behind of a whip-smart female scientist, but Leslie should have stuck around … because she was really mean to Leonard a lot of the time, and I sort of loved that.

Poor Janine Davis. The human resources manager at CalTech, played by Regina King, has her work cut out for her, especially where Sheldon Cooper is concerned; though Sheldon doesn’t necessarily mean to be offensive to women and other employees, he ends up in hot water for a variety of offensives, including telling a female subordinate that women are like egg salad left out on a hot Texas day (“full of eggs and only appealing for a short time”). Janine is constantly forced to step in and try to explain to Sheldon why saying something like that is absolutely unacceptable, but pretty much every time she tries, Sheldon ends up digging his grave even deeper. (While being asked to apologize for telling a woman that she’s a “slave” to her sexual desires, Sheldon makes a slave joke about Janine, a Black woman, and it does not go well.)

Like Christine Baranski, I have to imagine that King, an Oscar and Emmy-winning actress, producer, and director, simply didn’t have time to play Janine Davis all that often, but that’s a shame — because she was, at the end of the day, a phenomenal foil for Sheldon and a welcome presence on “The Big Bang Theory” every time she deigned to show up. Again, I’m sure the producers would have loved to feature King way more, and it was a matter of scheduling, but in any case, Janine definitely should have gotten more screen time somehow.

“The Big Bang Theory” is streaming on HBO Max now.