Penny

Penelope "Penny" (surname currently unknown) is Leonard Hofstadter and Sheldon Cooper's neighbor in 4B (across the hallway) in their apartment building.

Penny is the one of the main female characters in the show alongside Bernadette Rostenkowski and Amy Farrah Fowler, as well as the first of the three on the show. She has been Leonard's love interest from the first season until now, with the two characters dating at the time of the first season cliffhanger and for most of the third season. Despite the failure of the relationship, Leonard and Penny appear to be good friends and she still remains within the social group of the guys, although the relationship began again starting in the 100th episode.

Physical Appearance
Penny is frequently referenced by the other characters as being incredibly attractive, a fact she seems to be aware of already. Penny has blonde hair and green eyes. Wolowitz describes her as a "cheesecake-scented goddess". This description is fairly accurate, considering Penny is a waitress at the local Cheesecake Factory. Penny's height is 5'5", a fairly above average height. It is mentioned by Sheldon in The Adhesive Duck Deficiency that she has the Chinese character for "soup" tattooed on her right buttock.

Background
When she first met the guys in the Pilot, she was writing a movie about a girl from Lincoln, Nebraska, who travels to Los Angeles to become an actress but ends up working at The Cheesecake Factory instead. When Leonard asks if the movie is autobiographical, she replies no because she's from Omaha, Nebraska. The reason Penny is in the apartment building in the first place is because she split with her boyfriend of four years, Kurt, and was thrown out of their place. She says she still loved him, but wanted custody of their television set. The shower in her apartment was broken at the time, much to Leonard and Sheldon's friends' delight (she used Leonard and Sheldon's shower and came out wearing nothing but a towel!). She's either ignorant of or all too aware of her effect on the boys, because within minutes of meeting them, she asked Leonard to retrieve her television set from her ex-boyfriend's apartment, which he immediately sets out to do. Penny is aware of Leonard's crush on her, and it is hinted throughout the series that some of the feelings are reciprocated. They later start dating and doing "stuff."

She is sloppy and disorganized, but appears to like it that way. Whenever Penny goes on a rebound relationship, she picks up an attractive man and then has 36 hours of meaningless sex over the course of a weekend; afterward, the relationship deteriorates. At the end of season one, Penny goes on a date with Leonard. They are both very nervous, but share a passionate kiss, nonetheless.

In Season Two, there is some initial ethusiasm between Penny and Leonard. However, later, they both develop insecurities concerning their relationship. Penny is worried that she isn't smart enough for Leonard and lied about graduating from community college because she felt insecure. The relationship quickly deteriorates and she goes back to dating different guys.

She gives Leonard relationship advice when he's with Stephanie and they seem to develop a deeper friendship. She also starts to become geekier. She makes references to Star Trek, much to her own surprise, and plays Age of Conan. She also dates Stuart, who runs the comic book store. This annoys Leonard who thinks he and Stuart are pretty much the same person. When Penny and Stuart are making out she accidentally calls him Leonard and as a result, they stop seeing each other. This hints to her feelings for Leonard. When she learns he is going to the Arctic, she is visibly upset, she buys him a blanket with sleeves and tells her door, after speaking with Leonard, she wishes he wasn't going.

In Season Three, when the boys get back, she has obviously been missing Leonard quite a bit and kisses him passionately the second she sees him. Their relationship has a rocky start because first, they aren't left alone to be together, and second, they seem to have some trouble getting used to being more than friends. They eventually start a stable relationship, which annoys Sheldon. Sheldon applies his knowledge of behavioral psychology and begins to train her using positive reinforcement techniques—i.e. chocolate—with a surprising amount of success. Leonard disapproves of this manipulative behavior and gets a dose of Sheldon's negative reinforcement techniques i.e. a squirt bottle.

Family
So far, the only member of Penny's family that has been seen is her father, Wyatt. Penny had a very close bond with him when she was a child, however, it is mentioned that it was a tomboy bond since he wanted another son instead of another daughter, so despite hating to get dirty, Penny tried to be good at sports. He used to call her 'slugger' until she bought her first training bra, and he just stopped calling her 'slugger' and didn't play catch with her anymore. Several other members have been mentioned too. Penny's sister is also mentioned, as having shot her husband, whilst both she and the husband were drunk.

It is known that she has a nephew who turned 13 in the second season, and it's likely that he is the son of Penny's sister, as her sister is known to be married. When Christy comes into town, Penny reveals that she has a brother and at least one male cousin, as she claims that Christy slept with the former while being engaged to the latter. Her brother also works in a meth lab. This is first hinted in The Pirate Solution as Penny describes him as 'kind of a chemist' and told Leonard that he'll like him. It is finally confirmed in The Rhinitis Revelation, as she asks God to make her brother stop making it, but no cops. Sheldon implies Penny's mother is fat and she says that her mother used to smoke pot when she was pregnant with Penny.

Leonard
Leonard and Penny's relationship is one of the primary topics in the series. Leonard became attracted to Penny the moment he met her and it didn't take her long to figure out that he had feelings for her. Penny shows no signs of interest in Leonard until The Hamburger Postulate when she hears of his failed attempt at a relationship with Leslie Winkle, though the sign is seen only by the audience. Despite these signs, she continues to date other men as Leonard continued to try and make her give him a chance. It isn't late in the first season that her and Leonard date, however they break up not long after when Penny fears he will get bored with her due to his high intelligence compared to her own. They remain friends although signs of their feelings for each other continue to show. After Leonard returns from his 3 month research trip at the north pole Penny immediately kisses him, having missed him greatly. They begin dating again and despite another rocky start, they are together for most of the 3rd season. They break up again after Leonard says he loves her and she doesn't say it back. They again stay friends throughout season 4 but it is strained as Penny struggles to control her feelings for Leonard as well as her jealousy towards Priya. While drunk, she admits to Raj that she shouldn't have ever broken up with Leonard.

On the spur of the moment in "The Recombination Hypothesis", Leonard asks Penny out on a date after he imagined what getting back with her might be like. Their real date ends successfully and they agree to take their relationship slow in "The Beta Test Initiation". In later episodes they appear to be still together.

Sheldon
Penny and Sheldon constantly irritate each other and get on each other's nerves. Sheldon is quick to take shots at Penny's intelligence, job, and seemingly failing career while Penny throws off his personal routines. Despite their differences, Sheldon and Penny are very close, and are quick to help each other. They have taken care of each other on multiple occasions, often times doing things they really don't want to do to make each other feel better. Major examples are when Penny takes care of Sheldon when he is sick and when she lets him stay at her apartment when he gets locked out, even letting him sleep in her own bed. Sheldon was also quick to come to Penny's aid when she called for help after falling in the shower and dislocating her shoulder, going so far as to drive her to the hospital, despite not knowing how to drive. Many of these occurrences end with Penny singing the song "Soft Kitty" to Sheldon to make him feel better; Sheldon sang it to her on one occasion as well. One of the biggest examples of their friendship is that despite his own rule of avoiding physical contact with people, Penny is one of only 3 people Sheldon has hugged who aren't members of his family. The only others being Wil Wheaton and Amy Farrah Fowler. Penny seems to at times act like a "surrogate mother" to Sheldon, with Leonard being the father. During the time Penny and Leonard were together, whenever they fought, Sheldon would act like a child who doesn't want his parents to split up.

Howard
Upon meeting, Howard constantly hit on Penny in ways that made her deem him "disgusting." Their dynamic remains the same for the most part throughout the series but begins to change when Howard begins to date Bernadette. Although Penny is not a fan of him, she and Howard maintain a friendship, although they rarely hang out outside the group. Howard flirts with Penny much less and becomes more casual towards her after he begins his relationship with Bernadette, which Penny obviously enjoys, although she still pokes fun at him.

Rajesh
Like all other women, Raj was and is unable to speak to Penny unless he is drunk or on medication. They hangout within the group a lot and Penny occasionally attempts to tease him into talking to her. Raj begins to like Penny as the series goes on and the two end up getting drunk and appear to have slept together. Later Raj tells Penny that they did not have sex to her relief. Raj attempts to actually date her but she tells him she just wants to be friends. Despite their rough past, Penny attempts to find a girlfriend for Raj and comforts him when he may need it.

Bernadette
Penny and Bernadette work together at the Cheesecake Factory and are close friends. She is the first person outside of the main group that Penny is seen to hang out with on a regular basis. They enjoy hanging out at Penny's apartment and going out together. They also hang out with the guys together once Howard starts dating Bernadette.

Amy
When Bernadette and Penny were having a sleepover, Amy injects herself into Penny's life by getting herself invited. In no time she claims that she and Penny are best friends and calls her "bestie". When she initially hangs out with Penny and Bernadette her lack of social skills make it somewhat awkward, but as she spends more time with them they bond and the 3 become their own group within the group of guys. The two gradually form a tight friendship and continue to spend more time together and are quick to aid one another whenever the other needs it. Amy is aware that Penny is the planet that her social life revolves around and quickly reverses her course if she is mad at her or is annoying her. Amy gave Penny a lage ugly picture of the two of them to celebrate their friendship. At one point she realizes that Penny hates it, Penny rushes over to Amy's apartment to rescue their friendship and rehangs the painting in her apartment.

Trivia
only overcame her addiction when she realised she'd accepted a virtual date from Sir Howard of Wolowitz (Howard).
 * In the Episode "The Pancake Batter Anomally" Sheldon calls Penny 'Typhoid Penny' he is refering to Typhoid Mary who was a chef and spread typhoid through her food.
 * Penny is 22 years old at the beginning of the show (in the early fall of 2008, when The Barbarian Sublimation aired), which means that she is the youngest of the Gang. Penny is a Sagittarius, meaning she was born between November 21 and December 22. In The Prestidigitation Approximation, Howard does a fake magic card trick in which you take the sum of the digits of one's birthdate, excluding the year, to get the number of the card you have to turn over. Penny turns over the fifth card, making her birthday in the span of the Sagittarius one of four possibilities: November 30th, December 2nd, December 11th, or December 20th. Penny's birthday likely is November 30th (1+1+3+0=5), as it would match the birthday of Kaley Cuoco (Saturday, November 30, 1985) exactly. Observe that the only possible birthdate of Penny would be Monday, December 2, 1985 if one alternatively interprets the rules of Howard's card trick as requiring one to turn over the card corresponding to the sum of the digits of the month and adding the day. Though, David Underhill refers to Penny as a "gorgeous 22-year-old" in The Bath Item Gift Hypothesis (airdate December 15, 2008), he could have simply estimated her age, as it certainly appears to be close to Christmas and the episodic events probably span days rather than weeks (if one were to ignore the hypothesis that the airdate is reality in the show).
 * Sheldon once calculated that Penny dated an estimate of 193 (±8) men and had sex with approximately 31 men.
 * Penny grew up on a farm and rebuilt an entire tractor engine all by herself when she was 12.
 * She was Junior Rodeo champion.
 * Leonard and Sheldon's previous neighbor before Penny was a 200 pound transvestite named Louie/Louise with a skin condition according to Sheldon.
 * She is the only member of the main set of characters whose last name has not been spoken or revealed, but Bill Prady has said it eventually will be.
 * Penny claims to be a vegetarian but will eat fish and "the occasional steak. I love steak!"
 * Penny often smells like either vanilla (because she wears vanilla oil) or cheesecake (because she works at The Cheesecake Factory).
 * Penny has a sister, who once shot her own husband. They were both drunk.
 * Penny also has a brother, who slept with her friend Christy (who everyone refers to as 'the whore of Omaha'). She once says he's 'kind of a chemist' which probably means he's a drug dealer (most likely Meth), because it is mentioned at the same time as she mentions his court date.
 * She is very good at Halo the first time she plays it, which makes Sheldon extremely angry, because she beats him and he is a very sore loser.
 * Penny lives in apartment 4B.
 * Penny eats Chinese food with a fork and double dips her egg rolls (unappealing attributes, according to Sheldon).
 * Penny barely classifies her friend Christy as a friend because "friends don't get their friends' Care Bears all sweaty" (Christy and Howard had sex on them).
 * Her father used to call her "Slugger" until she got her first training bra, after that she wasn't "Slugger" anymore
 * Penny once got addicted to Age of Conan where she played as a Guardian named Queen Penelope and
 * In The Staircase Implementation, it is revealed that Penny was almost a teenage mom.
 * She mentions in Season 2 that she is 22 and she has a nephew who is 13.
 * Penny is very kind, but can become extremely fierce when provoked. She has yelled at Sheldon, Raj and Howard when they annoy her too much, and Leonard when she's angry.
 * Penny dated Leonard during most of Season 3. The relationship eventually came to an end during The Wheaton Recurrence after Leonard told Penny he loved her and she was unable to tell him she loved him too. They decided during The Spaghetti Catalyst that they able to stay as friends (for Sheldon's sake).
 * When under pain medication, she becomes almost as annoying as Sheldon (conjecture).
 * Penny believes in psychics, ghosts, astrology, voodoo, and other beliefs and traditions.
 * A reference to what may supposedly be her full first name was made in The Barbarian Sublimation, in which her online nickname to play Age of Conan was Queen Penelope.
 * She is from a little farm town outside of Omaha, Nebraska.
 * Penny is known to be very untidy. Sheldon once broke into her apartment to tidy it.
 * Penny went to community college, but dropped out for unspecified reasons.
 * The running gag of the show involves Sheldon knocking Thrice and saying "Penny". He repeats this thrice or until she answers the door. This is one of the most frequent scenes in the show.
 * She admits a couple of times that she screwed up with Leonard by leaving him.
 * Whenever Priya says something bad about Penny, she says "That bitch!"
 * She is jealous of Priya for appearing to be a more suitable girlfriend for Leonard than she was since not only is Priya beautiful and attractive, she is also intelligent and is highly-accomplished in her field of career.
 * According to Howard, he must obtain more than 1000 condoms for him to engage in coitus with Penny.
 * She had drunken sex with Leonard and Raj (Raj later revealed to Penny that they did not actually sleep together but keep it between them so Raj can save face) in last episodes in third and fourth season, furthermore both misunderstood that. It's unknown if this is coincidental or on purpose.
 * With the exception of his family, Wil Wheaton, and Amy Farrah Fowler, Penny is the only person Sheldon has hugged.
 * Penny is known to be a moocher. When Sheldon's mom pointed out her disapproval of a piece of top belonging to Penny, she said that she had received free drinks by wearing that top. It is also known that while she was dating Leonard, she never paid for her movie tickets. She also gets free meals from hanging with the guys since her portions were always paid by Leonard, she said they were loans but deep down she knew Leonard would not ask her to pay back. She also gets free internet by using Sheldon and Leonard's Wi-Fi - which leads Sheldon to regularly change the password to ones which accuse her of freeloading.
 * She turned down Sheldon's offer for a date (although Sheldon only asked her to make Amy jealous) and revealed that her mother smoked pot while pregnant with her in The Flaming Spittoon Acquisition.
 * Penny was actually a bully in high school, making fun of a girl with a stutter and taping another girl up and leaving her out until the next morning.
 * In Sheldon's attempts to get information or help from Penny, he usually ends up insulting her when referring to her personality or actions.
 * At Comic Con, Kaley Cuoco was on the Big Bang Theory panel and explained that Penny was in love with Leonard, but doesn't realize it.
 * Penny is remarkably adept at games in general, excelling at Halo, Age of Conan, and most recently Chess, check-mating Leonard on her first try( though the latter may have been because, as Sheldon has pointed out, Leonard is terrible at chess).