The Big Bang Theory: The Biggest Changes From The Unaired Pilot

"The Big Bang Theory" enjoyed a 12-season run as one of the most popular sitcoms on television, but you might not know that the pilot that ultimately aired on CBS wasn't creator Chuck Lorre's first attempt at the project. That unaired original pilot? It's pretty weird, objectively bad, and very different from the show most fans recognize.

In the pilot of "The Big Bang Theory" that made it to air, Sheldon Cooper (Jim Parsons) and Leonard Hofstadter (Johnny Galecki) head home from an "errand" — they try to donate sperm to a "high-IQ" bank, only to panic and run — to find their new neighbor Penny (Kaley Cuoco) moving in across the hall. Leonard is immediately smitten with Penny, much to Sheldon's consternation, and he readily invites her into their apartment to meet their friends Howard Wolowitz (Simon Helberg) and Raj Koothrappali (Kunal Nayyar, who almost didn't even end up playing Raj in the first place) and eat some lunch. From there, Leonard's pursuit of Penny escalates as he tries to get her TV back from an ex-boyfriend, at which point Sheldon (sort of) accepts that she's part of the group now.

Okay, so let's step back: what happens in the strange original pilot, and how is it different from what we all ended up seeing? From a radically different take on Penny to the music to the set, here are all the things that changed after the first "Big Bang Theory" pilot crashed and burned.

Not only is Penny not in the original pilot of "The Big Bang Theory," but there's an entirely different female foil for Sheldon and Leonard ... and she sort of sucks, actually. After successfully donating to the sperm bank, the two stumble across Katie — played by Amanda Walsh — who's arguing with her mom on the phone while sitting on the curb (at which point we learn that Katie slept with her stepdad before he married her mom). Leonard invites her out for dinner, at which point she starts to soundly taunt both guys about how bad they are at talking to women. While she does have a point, the fact is that Katie bears little resemblance to the Penny we meet in the pilot (who makes fun of the guys but isn't quite as vicious) — and audiences hated her, apparently.

As Chuck Lorre and fellow co-creator Bill Prady told  Entertainment Weekly in 2022, test audiences really didn't like Katie and really went to bat for Leonard and Sheldon as a result. "They were very vulnerable, and the audience didn't want a toxic presence around them," Lorre explained. "That's why we rewrote Katie to become Penny [Kaley Cuoco] and made her much more charmed by the guys and kind to them, as opposed to a woman who would take advantage of them." (He also went to bat for poor Walsh, saying, "She was terrific in the role, but the role was misconceived. It was our responsibility.") Unfortunately for Walsh and fortunately for Kaley Cuoco, they re-engineered the character, and we got Penny.

The Sheldon Cooper fans know from the entirety of "The Big Bang Theory" is basically asexual, but that's definitely not the case in the unaired pilot. While they're at the sperm bank, Sheldon goes on at length about how much he liked a magazine that featured women with big butts (before going on a more typical Sheldon rant about how women with large posteriors are the best biological choice for mates). At one point, he tells Leonard exactly how many nude women he's seen before in his life (it's six) and towards the end of the pilot, when Leonard and Sheldon's friend Gilda (Iris Bahr, and we'll come back to that character in just a bit) shows up to their apartment, it's revealed that she and Sheldon have hooked up a bunch of times.

Obviously, this bears little to no resemblance to the Sheldon Cooper in the legitimate pilot, and it's almost baffling to see a horned-up version of Sheldon. In the full series, Sheldon isn't intimate with anyone until he meets Amy Farrah Fowler (Mayim Bialik), and even then, it takes a really long time for him to open up to her physically. This strangely sexualized Sheldon who's also completely incapable of interacting with women doesn't work — clearly.

Like most sitcom characters, everyone on "The Big Bang Theory" resides in sizable and well-lit apartments that they probably wouldn't be able to afford in real life, and the core gang on "The Big Bang Theory" spend quite a bit of time hanging out in Leonard and Sheldon's living room. In the unaired pilot, though, it sort of looks like a hellhole.

The lighting in the original pilot, it should be said, is bizarrely dark, to the point where it almost strains your eyes to look at it, and when Katie, Leonard, Sheldon, and Gilda are all at the boys' apartment, it's poorly lit and looks quite different. (It's also notable that the couch, on which Sheldon has claimed one specific spot, isn't the same leather one from the rest of the series.) It's fair to assume that the unaired pilot didn't have an enormous budget, which could explain the lighting and different apartment, but it's still really jarring.

You might have noticed that Howard and Raj, two of the main characters on the series, haven't come up in a while. That's because they're not present at all during the original pilot of "The Big Bang Theory." Gilda is the only friend of Leonard and Sheldon that we actually meet, and the pilot absolutely feels like it's missing something without either Raj or Howard there, largely because Katie's pretty mean and Gilda comes on pretty strong (again, we'll circle back to good old Gilda).

It's a good thing that Chuck Lorre and his creative team brought Howard and Raj into the mix, because they're perfect additions to Leonard and Sheldon's (admittedly limited) social circle. Sure, Howard starts the series out as a total creep (he gives Penny a teddy bear with a camera in it, as just one example), but he grows up a lot — and without him, we might never have gotten to meet Bernadette Rostenkowski, played by Melissa Rauch. Raj is saddled with some pretty odd issues in the beginning of the series, including selective mutism around women, but he's one of the show's sweetest characters. The show would definitely feel lacking without Howard and Raj, because the unaired pilot doesn't feel right without them.

The apartment building's broken elevator is a whole thing in "The Big Bang Theory." Penny, Leonard, and Sheldon — and later, Amy — all have to hoof it up and down several flights of stairs to get to and from their apartment, which is basically a narrative device that encourages frequent walk-and-talk scenes. (Apparently, the creative team behind "The Big Bang Theory" is unfamiliar with "Grey's Anatomy," where a lot of really wild stuff happens in elevators — but that's another matter altogether.) The series finale ultimately includes a moment where, as Leonard and Sheldon chat in the hallway, Penny arrives in the mysteriously mended elevator and even convinces an apprehensive Sheldon to ride it with her.

Not only is there no mention of an elevator — broken or otherwise — in the unaired pilot, but it's definitely not a focal point like it is in the original series. It doesn't seem like the biggest omission if you're not super familiar with the show, but the elevator ends up being a huge deal in "The Big Bang Theory," so its absence is still notable.

Much like the elevator thing, the music in the unaired pilot is completely different, and while it feels small, it's really jarring if you're familiar with "The Big Bang Theory" and its complete earworm of a theme song. The track — titled "History of Everything" — is performed by the Barenaked Ladies and runs through a brief history of the universe, as advertised; during the closing credits of each episode, an instrumental track with the same tune always plays. (Scene changes are simply marked by a "whooshing" sound.)

The unaired pilot uses a different song, though, and it's ... odd. Instead of "History of Everything" — which was actually written for the show at Chuck Lorre's request — the show used a song that already existed. The song in question? "She Blinded Me With Science" by Thomas Dolby. It's kitschy in all the wrong ways and just makes the entire conceit feel extra-weird. It's a good thing that the Barenaked Ladies ended up stepping in.

We're finally circling back around to Gilda, the deeply strange fourth member of the initial "Big Bang Theory" cast. Much like Howard and Raj, Gilda is just sort of ... around, and it's revealed that not only has she slept with Sheldon, but she's carrying a torch for Leonard — which is why she hates Katie when she comes over to their apartment. The dynamic between Gilda and the two guys doesn't feel natural at all, and her rivalry with Katie feels extra forced. Gilda didn't stick around, but it does feel like she influenced two characters who eventually became big parts of the show.

Considering that Gilda does appear to work with Leonard and Sheldon, it's easy to assume that she shares at least a little DNA with Leslie Winkle (played by Johnny Galecki's former "Roseanne" castmate Sara Gilbert), who works at CalTech with the rest of the guys and makes her first appearance in season 1. Later, the series introduced Mayim Bialik's Amy Farrah Fowler, a socially awkward scientist who ends up marrying Sheldon, and she also bears a passing resemblance to Gilda. Unfortunately for Gilda, she didn't get to stick around, but she was definitely influential.