[Spoiler Alert! At the end, there are some plot lines revealed for first three seasons].
In 2006, The Big Bang Theory premiered on CBS. At the time, it seemed like an interesting concept for a series: a group of four nerd friends who are brilliant at their jobs and their passions (TV shows, movies, comics, and video games considered “geeky”) but incompetent in other equally important areas like social interaction and finding a romantic relationship. Sheldon, who desires order and typically has no regard for social rules, would stick his nose up at romantic relationships, considering them a waste of time. Howard went in the opposite direction and is constantly coming on to the ladies, with no regard for their feelings; thus, he typically strikes out. Raj, however, has such a crippling fear of being around women that he can’t even speak around them except with alcohol. Leonard, the most socially aware of the bunch, still struggles in social situation to keep from embarrassing himself.
Into this world comes Penny, the girl who lives across the hall from Leonard and Sheldon. She is a waitress trying to make ends meet while looking for any acting job. A gorgeous blonde, this woman may not be as intelligent in smarts as the four main characters, nevertheless is well aware of social situations and social cues, and can navigate more successfully in the outside world. Case in point: in the season three episode, “The Cornhusker Vortex,” Penny is shown to have many friends who watch football with her and enjoy the game with her. However, she is not without her own flaws: she is a serial dater, constantly giving into shallow but handsome men who will give her attention (this does not go unnoticed by Leonard, who is in love with Penny). Also, while Leonard and Sheldon’s apartment is immaculately clean, her apartment is constantly messy with clothes thrown everywhere.
When Penny first moves to the apartment across the hall in the pilot, she asks as a favor for Leonard and Sheldon to get her TV from her boyfriends’ place, realizing of course the awkwardness of having to collect your things from your ex. Leonard, infatuated with Penny, convinces Sheldon to go along with the foolhardy errands’ run, but their reasoning falls on deaf ears to the incredibly buff ex-boyfriend of Penny’s, and they return without the TV…and without pants. Someone with no social grace would have just been angry at Leonard and Sheldon for failing to return with the TV. But Penny, feeling bad about the situation, once again realizes that she should show her appreciation to the two guys for what they did, and offers to give them dinner.
This is what begins her friendship with the four friends. She becomes at times “one of the guys,” coming over for takeout on many occasions and willing to engage in some of the same hobbies and interests, like Halo. But eventually, Leonard makes Penny aware of his feelings toward her. While admittedly not attracted to his physical attributes or his intelligence, Penny is however attracted to his sweet and caring nature toward him versus the guys who usually date her. They go on a date at end of the first season, but quickly break up in the beginning of the second because Penny is fearful that she is “not smart enough” for him. However, again, it is Leonard’s constant caring nature and good heart that enable Penny to fall for him when the four go on a scientific mission to the arctic at the end of season three. She didn’t even know how much she missed and loved him until he told her he was leaving. Leonard and Penny begin a real long term relationship in season four.
What makes Penny so great is that she is the opposite in some ways the four guys, but she is not dumb. She is socially intelligent in other ways and that shows, and she is not afraid to also let off a sarcastic (but typically not insulting) comment when she recognizes one of the guys’ social awkwardness. She is shown as a flawed but interesting individual, who has a good heart but is capable of making bad judgments with the men in her life. Just like Leonard, Sheldon, Howard and Raj, she is a three-dimensional character, and the show is better because of her in it.