and executive produced by Chuck Lorre and Bill Prady, premiered on CBS on September

24, 2007. The show initially centers on five characters: roommates Sheldon Cooper and Leonard

Hofstadter, two Caltech physicists; Penny, a waitress and aspiring actress who lives

across the hall; and Leonard and Sheldon's friends and co-workers aerospace engineer

Howard Wolowitz, and astrophysicist Rajesh Koothrappali. In Season 3, microbiologist

Bernadette Rostenkowski, and neuroscientist Amy Farrah Fowler are introduced, and later

become Howard's wife and Sheldon's girlfriend, respectively.

Over time, several supporting characters have been promoted to starring roles: Leslie Winkle

(season 1 recurring; season 2 regular; season 3 guest), a physicist colleague, and, at different

times, a lover of both Leonard and Howard; Bernadette Rostenkowski-Wolowitz (season 3

recurring; season 4-present regular), a microbiologist, Howard's fiancée and subsequent wife, and

former part-time waitress alongside Penny; neuroscientist Amy Farrah Fowler (season 3

guest; season 4 recurring; season 4-present regular), who joins the group after being

matched to Sheldon on a dating website; and comic book store-owner, Stuart Bloom (seasons

2–5 recurring; season 6-present regular), who replaces Howard as Raj's best friend when

Howard is in space. The show also features numerous supporting characters, each of whom

plays a prominent role in a small group of episodes.

Main characters Main characters are divided into two groups,

original main characters and those who have been promoted to main character status since

season two. Original main characters

With the exception of injury to the actors, these characters have appeared in all episodes.

Leonard Hofstadter Dr. Leonard Leakey Hofstadter (Johnny Galecki)

is an experimental physicist with an IQ of 173 who is originally from New Jersey and

received his PhD at age 24, spending at least some of his time at Princeton University.

He shares an apartment in Pasadena with colleague and friend Dr. Sheldon Cooper. Unlike his

equally geeky friends, Leonard is interested and quite adept in building interpersonal

and social relationships with others. Compared to his friends he is relatively successful

with women. The writers have toyed with a romance between him and next-door neighbor

Penny since the pilot, with their unresolved sexual tension being a major force for drama.

Leonard dated Penny for most of Season 3, although they had dated briefly at the end

of Season 1. Aside from Penny, Leonard has had romantic relationships with coworker Leslie

Winkle, physician Stephanie Barnett, an unnamed French literature PhD, and North Korean spy

Joyce Kim. Following his breakup with Penny, Leonard began a relationship with Raj's sister

Priya in Season 4, and it is implied they had a brief sexual encounter before the start

of the series on an occasion when Priya visited Raj. The two attempted a long-distance relationship

after Priya moved back to India, but Leonard eventually broke up with her in Season 5 after

she admitted to cheating on him with her former boyfriend. In Season 5's "The Beta Test Initiation",

Leonard and Penny start dating anew though their relationship is rocky. Leonard's family

includes other accomplished scientists: his mother, Dr. Beverly Hofstadter, is a world-renowned

psychiatrist, his sister is a biologist and his father an anthropologist. Also, his brother

Michael is a Harvard law professor. It is mentioned in the season 2 episode "The Maternal

Capacitance" that Leonard is the least successful member of his family. He is also known to

be lactose intolerant and cannot process corn, as Sheldon states in "Pilot". Leonard also

plays the cello. The cause of the elevator not working is also due in part to Leonard

(and Sheldon) as the experimental rocket fuel he was developing was improperly mixed within

their apartment and Sheldon threw the canister into the elevator shaft right before the explosion.

Sheldon Cooper Dr. Sheldon Lee Cooper (Jim Parsons) is a

theoretical physicist, possessing a Bachelor of Science, Master of Science, PhD, an ScD,

and an IQ of 187. Originally from East Texas, he was a child prodigy, starting college at

the age of 11, and receiving his PhD at age 16. He is cold and calculating, and refrains

from any form of physical contact if possible. Sheldon exhibits a strict adherence to routine

to the point of exhibiting obsessive–compulsive disorder, performing specific activities on

specific days and specifics times, such as doing the laundry on Saturday night at 8:15.

Any disruption to this routine distresses him enormously. A running gag has him always

knocking on doors or other surfaces in a pattern of three knocks and one call repeated three

times, which he has to complete no matter what. He has forced Leonard into signing an

absurdly exhaustive "Roommate Agreement", and later enters a similar "Relationship Agreement"

with Amy Farrah Fowler. Sheldon has great difficulty identifying sarcasm and irony and

responding in kind, and a recurring topic is his efforts to acquire these skills. He

has also enormous difficulties lying or even keeping a secret, giving himself away with

wild facial tics and implausible statements. He is however fond of occasionally playing

a prank, which he typically punctuates with his trademark exclamation "Bazinga!". Sheldon

has a superiority complex and makes no effort to hide his contempt for other people's intellects,

often making highly inappropriate comments. A common joke is his inability to drive, although

he did receive a learner's permit. Sheldon loves comic books and science fiction like

his friends, but to the point of being obsessed about them, and is a fan of Spock, a fictional

character of the Star Trek franchise. Unlike Leonard and Raj who come from intellectual

families, Sheldon stands out from his own relatives. His father, George, whose death

pre-dates the series, was described as a stereotypical Texan who liked football, skeet shooting,

and heavy drinking, his mother, Mary, is a devout Evangelical Christian, who does not

possess anything near Sheldon's intellect (though she displays a great deal of common

sense); his twin sister, Missy, and as-yet unseen brother, George Jr., were both described

by Mary as being "dumb as soup". His fraternal twin sister who later has a baby boy makes

Sheldon an uncle. He meets Amy Farrah Fowler in the Season 3 finale and starts a highly

unusual and very slowly evolving relationship with her. Previous to this, he has also exhibited

some affinities with Leonard's equally unemotional mother.

Penny Penny (Her surname has not yet been revealed.)

(Kaley Cuoco), is Leonard and Sheldon's neighbor across the hallway. Originally from a small

town outside Omaha, Nebraska, she was a waitress and occasional bartender at the local Cheesecake

Factory until season 7 and is an aspiring actress. Her educational qualifications (she

had dropped out of community college) are a constant source of disparaging comments

from Sheldon. She has dated several men during the course of the series, including Kurt,

Stuart, and Zack, but her recurring love interest is Leonard. Leonard pursued Penny during season

1; they dated briefly at the start of season 2 which led to some awkwardness; they began

dating again and were a couple for most of season 3 but she broke up with him after he

told Penny he loved her and she was not ready to reciprocate. Penny and Leonard begin to

date again "slowly" during the fifth season, though he does upset her by impulsively asking

her to marry him during intercourse. She has a tense relationship with Sheldon, whose nerdy

and obstinate personality often exasperate her, but they are ultimately good friends,

helping each other out in various situations. By season four, Penny also begins to socialize

more with Bernadette and Amy, who frequently hang out in Penny's apartment, go out together

and comfort each other. Bernadette and Amy are both shown to be simultaneously envious

of and threatened by Penny's more outgoing personality. Not much is known about Penny's

family, but it is mentioned in the series that her father, Wyatt (portrayed by Keith

Carradine), raised her like a boy, her mother smoked marijuana while she was pregnant with

her, her sister shot her husband while they were intoxicated and her brother is a meth

addict. Cuoco began being credited as Kaley Cuoco-Sweeting, starting with the season seven

episode, "The Convention Conundrum". Howard Wolowitz

Howard Joel Wolowitz (Simon Helberg) is an aerospace engineer at Caltech's Department

of Applied Physics with a Masters in Engineering who often hangs out at Leonard and Sheldon's

apartment. Unlike Sheldon, Leonard, and Raj, Howard has no doctorate, and often gets disparaged

as a result, especially by Sheldon. He defends this by pointing out that he has a master's

degree in Engineering from MIT and that the equipment he designs is launched into space,

unlike the theoretical work of his friends. In the season 5 finale, Howard goes to the

International Space Station on Expedition 31. Howard lives in Altadena with his domineering,

belittling and unseen mother who treats him like a child. While he sometimes expresses

irritation at this treatment, for the most part he appears to prefer it. Howard dotes

on his mother and participates in many of her daily routines. A recurring gimmick in

the series is Howard and his mother communicating with each other from different rooms by yelling,

a habit which Bernadette also adopts in later episodes. His father left them when he was

eleven, and Howard gets visibly distressed when the subject comes up. Howard fancies

himself a ladies' man and attempts pick-up lines whenever a woman is present, which often

come off as inappropriate and disgusting, although he has dropped this habit since he

started going out with Bernadette. He is Jewish, but he is not very serious about his faith,

and does not keep kosher. For example, when the group's favorite Chinese restaurant raised

the price of pork, Howard remarked, "It's getting tougher and tougher to be a bad Jew."

However, he does observe Sabbath and the Jewish holidays. In the pilot episode, it is shown

that he is a polyglot and can speak English, French, Mandarin, Russian, Arabic, and Farsi,

along with fictional languages like Klingon and Sindarin. He is asthmatic, allergic to

peanuts, almonds, and walnuts, prone to canker sores and pink eye, succumbs to seasickness,

has an incredibly high genetic risk of heart illness, and has transient idiopathic arrhythmia.

In Season 5 episode 4, it is shown that he knows American Sign Language. Howard dated

Bernadette briefly in season 3. After some difficulties, they resumed their relationship

in season 4, which culminated in their engagement. In the season 5 finale, Howard and Bernadette

are married on the roof of the apartment building shortly before he has to leave for Kazakhstan

where he is to be sent to the International Space Station.

Rajesh Koothrappali Dr. Rajesh Ramayan "Raj" Koothrappali (Kunal

Nayyar) is Howard Wolowitz's best friend, and yet another genius of the group; his name

is usually shortened to "Raj". He is originally from New Delhi, India, and he works in the

Physics department at Caltech, where his area of expertise is particle astrophysics. He

lives in an apartment in Pasadena. As with his friends, he is mutually involved with

and obsessed with science fiction and comic books in general, and is usually the one to

propose various real-life questions derived from such works, such as the functions of

the tails of the Na'vi in the film Avatar. He is also a fan of Harry Potter. Raj dislikes

India, Indian food, and Indian music, he also appreciates the Indian lullabies his mother

sang to him and the catchiness of Hindi phrases. Raj is a Hindu and believes in karma (reincarnation),

but eats beef. Raj is very shy around women, and finds himself unable to speak to or while

in the presence of them unless he drinks alcoholic beverages, or he believes he has done so.

When Penny or Bernadette is around, Raj usually whispers what he wants to say to Howard or

Leonard, who then repeats or responds to what Raj says out loud, although at times Howard

will embarrass him by saying something completely different and inappropriate. Despite this,

Raj has sometimes ended up in bed with women, leaving the other guys perplexed. Unlike his

friends however, Raj has many quite feminine interests such as reading Archie Comics and

Twilight and watching chick flicks such as Bridget Jones's Diary. A recurring joke in

the series has people, including his parents and Leonard's mother, speculating that Raj

might be gay due to his feminine interests and his close friendship with Howard, with

whom he has arguments similar to those of a married couple. However, Raj has always

stated that he is straight, but metrosexual. He has had an infatuation with Penny, and

secretly wrote love poems about Bernadette. Raj comes from a very wealthy family in India,

and often communicates with his parents, Dr. and Mrs. Koothrappali, via webcam. He has

a younger sister, Priya, who is mentioned to have dated Leonard briefly before the series

timeline began and dates him again in Season 4, breaking up with him in Season 5. After

making a brave speech about not being embarrassed to be single, Raj started seeing a shy and

sweet woman named Lucy. Lucy has many things in common with Raj including her fear of being

in large crowds. In the season 6 finale, Raj finds he can now talk to women without alcohol,

however he never stops talking. Additional main characters

The following characters have been promoted to main character status since season 2. Leslie

Winkle and Stuart Bloom are only credited in episodes in which they appear. Bernadette

and Amy Farrah Fowler were promoted to main character status in season 4, and their images

were included in the main title sequence from the first episode of season 6.

Leslie Winkle Dr. Leslie Winkle (Sara Gilbert) (appeared

in eight episodes total, four credited as main cast) is an experimental physicist who

works in the same lab as Leonard. In appearance, she is essentially Leonard's female counterpart,

equipped with the black framed glasses and sweat jackets. She also happens to have a

lazy eye. She is one of Sheldon's arch-enemies, due to their conflicting scientific theories

and Sheldon's strong misogyny. Though they both consider each other to be intellectually

inferior, Leslie is much wittier than Sheldon, regularly calling him "dumbass" and besting

him in their exchanges. Leslie has had casual relationships with Leonard and later Howard,

considering it a completely physical reaction to her body's cycles - her voice remains emotionless

even during moments of extreme physical intimacy. Leslie's final appearance was in the season

3 finale, as the writers said they did not know how to work in the character full-time.

Leonard, distraught after Penny -- who after having broken up with Leonard got intoxicated,

had intercourse with him, then pushed him away -- asked for intercourse with Leslie.

Leslie responded, "Let me think about it," before slamming the door on him.

Bernadette Dr. (after "The Roommate Transmogrification")

Bernadette Maryann Rostenkowski-Wolowitz (Melissa Rauch): (has appeared in 64 episodes total,

59 credited as main cast) is originally a waitress and coworker of Penny's at the Cheesecake

Factory, which pays the way for her graduate studies in microbiology per "The Creepy Candy