CBSs most successful sitcom 'The Big Bang Theory' just got back on air doing season 9 and the question about Penny's (played by Kaley Cuoco) last name is still out there. According to Refinery29's website, the writers still didn't want her character to have a last name because they think it is actually funny. Penny has been in the picture for 9 years now and it is amazing how her last name was not used in a single episode of the show ever.
Vulture dared to ask show runner Steve Molaro about this enigma and if they would ever make Penny's last name known to its viewers, he answered it with, "You know, I don't think we will [reveal it]. We're kind of a superstitious lot here. We've made it this far without knowing Penny's last name. I think we're good not finding out." It is fascinating how they manage to be consistent about it and how they would like to remain mums about this issue.
The publication insisted on finding out about her last name that they gave out a hypothetical question saying; what if Penny becomes a famous actress since she is an aspiring actress on the show. Wouldn't the people want to find out about her celebrity name? But Molaro gave a safe good answering stating, "In general, I think what we have so far is a pretty accurate portrayal of a pretty girl who moved to Los Angeles, and took acting classes, and is trying, and is struggling, and is a waitress."
He continued with, "I think for a lot of people, that's the reality. If she starts to get really successful, now we're sort of behind the scenes in Hollywood, and I think that may be not exactly the kind of thing we tend to do on this show. But nothing's ruled out."
On the other hand, Penny now obviously has a last name since she married Leonard (played by Johhny Galecki), Molaro told THR.