Penny Hofstadter (née "Unknown") is the show's first and always main female protagonist. She lives in Apartment 4B with her husband Leonard Hofstadter across the hall from Sheldon Cooper, who lives in apartment 4A where Leonard used to live with Sheldon as roommates. Although the sleeping arrangements are a little complicated. This was an accommodation for Sheldon who was having a very hard time dealing with his break-up with Amy, and Leonard moving out in The 2003 Approximation. Leonard also maintains an office in 4A. Her full first name is possibly "Penelope" as implied by "The Barbarian Sublimation", and her maiden name has never been revealed. But due to her recent marriage to Leonard, her last name is Hofstadter. For a while her last name was Johnson while unknowingly married to ex-boyfriend Zack Johnson. That marriage was annulled in The Thanksgiving Decoupling.
An aspiring, but mostly unsuccessful actress, she was born on a farm near Omaha, Nebraska, and worked at The Cheesecake Factory as a waitress until she quit in "The Occupation Recalibration" (S7E13) to take up acting full time. Penny was the original female lead in the show before being joined by Bernadette Rostenkowski and Amy Farrah Fowler in seasons 3 and 4, and in season 8, started working at the same company as Bernadette.
She has always been Leonard's love interest since the pilot, with the two dating briefly in the first episode of the second season, for most of the third season, and they rekindled their romance in "The Recombination Hypothesis". As of "The Gorilla Dissolution", she and Leonard became engaged and were married at the start of season 9 in The Matrimonial Momentum.
Even though she is considered part of the guys' group, she represents the "dumb blond" for viewer context in the series with a lot of street smarts and communication skills to compensate for her lack of academic knowledge.
Penny is an slender, young women, with fair skin, blond hair and wears different types of clothing, mainly tank tops and jeans.
When she first moved into the apartment 4B, She was wearing a light blue tank shirt, blue denim shorts, and brown ugg boots.
Penny is somewhat naive and not thoroughly educated, but has a lot of common sense and street smarts. Her dream is to become a famous actress, a goal she never seems to waver from until season 8. She is very kind-hearted and empathetic toward people though she can blow up when made mad, which prompted Leonard to refer to her as The Incredible Hulk" after she went off on Howard. She believes most guys are nice and has been hurt a lot. When someone shocks her, she tends to bat her eyes at them while she is considering her response. She also walks away when frustrated with people like Sheldon or situations she can't believe or understand. She knows how to throw out wise-cracks and is very loyal to her man as long as she is not betrayed. She also has a tendency to deny doing things that are embarrassing or she suddenly realizes are embarrassing. In the first season she seemed very naive, but has appeared smarter in later seasons and more complicated in situations with her female friends. She also has a habit of being selfish and throwing her friends under the bus. For example, she sold Sheldon out to the court officials for running a red light, despite the fact he had done it to help her after she had dislocated her shoulder, simply because she didn't want the ticket.
Role in the Series
In the first episode Penny moves into Apartment 4B across from Apartment 4A where Leonard and Sheldon live. Penny had broken up with her boyfriend Kurt because he cheated on her. She asked the guys for a favor to go get her TV from his apartment, but he steals their pants and Penny apologizes for everything and later the three go out to dinner with Howard and Raj.
In "The Big Bran Hypothesis", Penny asks Leonard and Sheldon to sign for her delivery of her entertainment center. When Sheldon and Leonard, they discover that Penny's apartment is a mess, prompting Sheldon to try to clean it. When Penny arrives, they leave. Unbeknown to her at night, Sheldon cleans up the apartment anyway. When Penny wakes up the next morning, she is infuriated that Sheldon and Leonard came into her apartment while she was asleep, and forces Leonard to give back her spare keys. Sheldon forcefully apologizes to Penny and reveals that he cleaned her apartment. Penny bumps into Raj and she explains the situation, although Raj can't speak to her, he is a good listener, Penny decides to forgive Leonard, and when Leonard tries to apologize, she immediately forgives him.
After a post-date disagreement, Penny remains friends with all four guys, becomes an integral part of the Social Group and very good friends with Leonard.
In "The Hofstadter Isotope", Penny is asked out on a date by Stuart and things end later in the next episode after it is revealed she called Stuart "Leonard".
In the season finale "The Monopolar Expedition", Penny wishes Leonard wasn't going to the North Pole and even gives Leonard a blanket as a good luck gift on his expedition to the North Pole.
When the guys return from the North Pole, Penny has missed Leonard enough that she expresses her feelings for him and they date for most to the season.
Penny introduces her friend Bernadette to Howard as part of a Girlfriend Pact made between Howard and Leonard. Things don't go too smoothly until the two of them find out they both have overbearing mothers.
Penny resumes being part of the guys group and has her own friends, Bernadette, along with Sheldon’s new girlfriend, Amy. Also she realizes that she still has feelings for Leonard, especially since Leonard is dating Priya.
Half way through the season (on the 100th episode), Leonard asks Penny out and they reunite, though Penny has misgivings.
Penny works through her doubts and has a stronger relationship with Leonard, as she is now able to say "I love you" to him. They discuss marriage.
Penny finds out she is legally married to Zack after Leonard, Sheldon and Amy tell her that weddings in Las Vegas wedding chapels are real when the two thought they were fake. At the end, she and Zack fill out annulment papers and the marriage is legally annulled ("The Thanksgiving Decoupling"). Penny quits The Cheesecake Factory to concentrate on acting ("The Occupation Recalibration") and becomes engaged to Leonard after she gets over her clash with the director who fired her ("The Gorilla Dissolution").
Between the finale of Season 7 and the premiere of Season 8, Penny drastically changes her look by swapping her usual long blonde locks for a short blonde pixie-crop, a look she sports throughout the entire season. She gets a new job at Bernadette's company as a pharmaceutical rep, making excellent progress in her field as well as spending the year as Leonard's fiancée. At the end of the season, she suggests they head to Vegas to get married.
Leonard's little make out session at sea, makes their marriage have a rocky start, but they quickly reconcile though they don't move out of Sheldon's apartment (because of Sheldon going through a bad breakup, and due to Sheldon's abandonment issues). At the end of the season, when it's revealed that everyone is upset about not being part of the wedding due to their elopement, Penny suggests having a redo wedding ceremony.
In "The Conjugal Conjecture" Penny and Leonard have their re-wedding ceremony in a park which is officiated by Bernadette.
Penny and Leonard finally have their own apartment, Apartment 4A. In "The Cohabitation Experimentation", Amy's apartment suffered water damage, was uninhabitable and she needed a place to stay. Sheldon and Amy started a five week experiment to see if they could manage living together and moved into Penny's old apartment, Apartment 4B. It turned into a permanent arrangement in "The Veracity Elasticity". Penny also redecorates her and Leonard's bedroom.
While Sheldon is proposing to Amy, he gets a call from Leonard and Penny, asking about where he is. He tells them about his unwilling kiss with Ramona and how it made him realize his true feelings about Amy. At the same time, Bernadette tells Penny that she’s pregnant again.