The Big Bang Theory producer Steve Molaro officially debunks one theory about Penny's last name being secretly revealed on the sitcom. Played by Kaley Cuoco, Penny was the only female character from the show's original cast. Throughout The Big Bang Theory's 12-season run, Penny went through a lot both professionally and personally. By the series finale, Penny had a happy ending with a thriving career and a growing family with her husband, Leonard.
While The Big Bang Theory developed her arc from a struggling actress to becoming a happily married career woman, there's one thing that the sitcom failed to address regarding the character. CBS never revealed Penny's maiden name before she married Leonard. A fan theory, however, claims that the sitcom secretly resolved this mystery after spotting the name Penny Teller on a package that she received on the show. Unfortunately, that detail isn't canon.
As Molaro says in The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series (via TV Line), the theory that Penny's maiden name is Teller is simply not true. It isn't a detail that they intentionally hid in The Big Bang Theory hoping that fans will eventually find it. Read Molaro's full quote below:
"Props had to put a label on it and it happened to be caught on camera. We didn’t sanction it, we didn’t write it, and we didn’t intentionally put it there. Her last name being Teller is absolutely not canon. The canon is that she does not have a last name that we ever assigned to her… and we’re never going to make one. Even when she and Leonard got married, we made sure to edit around even hearing what her [last] name would be.”
Why Penny Never Got A Last Name
A previous comment from Molaro maintains that after they initially realized that her maiden name hadn't been revealed on the show, they decided to stick with it. Apparently, they "got nervous and superstitious and giving her [a last name]." So, until The Big Bang Theory wrapped up, it kept the detail a mystery. They deemed it inconsequential to the story of the sitcom that they didn't even have an official decision as to what it is. In any case, aside from people's curiosity, not resolving the mystery doesn't really have any impact on her and the show's overall narrative. What's important is that at the end of The Big Bang Theory, she was a Hofstadter.
For what it's worth, fans aren't the only people who are curious to know what Penny's last name is. Kaley Cuoco herself admitted that it was one of the things that she wanted to be resolved before The Big Bang Theory ended, with the other one being the busted elevator finally getting fixed. She got her second wish granted in the finale, but at this point, it's safe to say that the mystery surrounding Penny's surname will never be resolved.
Source: The Big Bang Theory: The Definitive, Inside Story of the Epic Hit Series (via TV Line)