The Big Bang Theory: 10 Questions That Must Be Answered Before The End
2. What Is Penny's Last Name?
By this point in the series, the audience knows the characters fairly well. There's Dr. Leonard Hofstadter, Dr. Sheldon Cooper, Dr. Rajesh Koothrappali, Mr. Howard Wolowitz, and Penny.... um... Penny... what's Penny's last name?
You might think you have heard her last name at least once during the series, but the name has never been revealed in any way. Not on any mail seen in her apartment or said by any character even once.
It isn't clear if she took Leonard's last name once they married, though it isn't believed that she did. Penny doesn't seem like the type of woman who would take the name of her husband as she is a proud member of the "we're not telling you her last name" clan.
With any luck, the series will conclude by finally revealing what her last name is. It could be in a joking way about how she did or did not take Leonard's last name as an aside or throwaway line. Whatever the series does, if it concludes without letting the world know what Penny's last name is, there might be rioting in the streets.