Penny

Penny is Leonard Hofstadter and Sheldon Cooper's neighbor across the hallway and is, as described by Wolowitz, a "cheesecake-scented goddess." This description is fairly accurate, considering Penny is a waitress at the local the Cheesecake Factory. She is also 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 recently split with her boyfriend of four years, Kurt, and was thrown out of their place. She says she still loves him but wants custody of their television set. The shower in her apartment is currently broken, much to Leonard and Sheldon's friends' delight (she now uses Leonard and Sheldon's shower and tends to wear 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 asks 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 is hinted throughout the series that some of the feelings reciprocates. They later start dating and doing "stuff". She is messy 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 none-the-less.

In season two there is some initial awkwardness between Penny and Leonard. This is brought on by their 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 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.

Trivia

 * Penny is 24 years old.
 * Penny is a Sagittarius but most people think that she's a water sign.
 * Penny grew up on a farm and rebuilt an entire tractor engine by herself before she was 12.
 * Leonard and Sheldon's previous neighbor before Penny was a 200 pound transvestite named Louie/Louise with a skin condition.
 * 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.
 * 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 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 mentiones his court date.
 * 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 only overcame her addiction when she realised she'd accepted a virtual date from Sir Howard of Wolowitz (Howard).
 * She has a tattoo of the chinese character for soup (possibly 汤?) on her right buttock. She thinks it means "courage."
 * Penny's last name has so far not been revealed.
 * 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 both Sheldon, Raj and Howard when they annoy her too much.
 * Penny was dating Leonard. They broke after Leonard said I love you and Penny did not say it back, she ran out the bowling alley crying and that was the end of their relationship.
 * When under pain medication, she becomes almost as annoying as Sheldon.