List of The Big Bang Theory characters
The American sitcom The Big Bang Theory, created and executive produced by Chuck Lorre and Bill Prady, premiered on CBS on September 24, 2007. The series 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. Over time, several supporting characters have been promoted to starring roles: In season 3, microbiologist Bernadette Rostenkowski, and neuroscientist Amy Farrah Fowler are introduced, and later become Howard's wife and Sheldon's girlfriend, respectively. Both were promoted to main cast in season 4. Stuart Bloom, a comic book store-owner who has been a recurring character since season 2, became a main character in seasons 6 and 8. Leslie Winkle, a promiscuous physicist who had an affair with Howard and Leonard on separate occasions, briefly became one of the main cast in season 2 before disappearing from the series.
The series also features numerous supporting characters, each of whom plays a prominent role in a small group of episodes. Included among them are parents of the main characters, their dates and their coworkers. Celebrities such as Stephen Hawking occasionally appear in cameo roles as themselves.
- 1 Character appearance summary
- 2 Original main characters
- 3 Additional main characters
- 4 Recurring characters
- 5 Minor characters
- 6 Notable guest stars appearing as themselves
- 7 Notes
- 8 References
- 9 External links
Character appearance summary
Characters are divided into four groups:
- The original main characters are five members of the ensemble cast who appear in all episodes, with the exception of Penny, who was absent from two episodes of season 4 because of Kaley Cuoco's physical injury.
- Additional main characters are those who been introduced to the series as the story was expanded. Leslie Winkle was only a main character for season 2, and Stuart Bloom was a recurring character in season 7, regaining main character status in season 8. All of the other additional main characters have retained this status after being promoted to main character status. Leslie and Stuart are only credited in the episodes in which they appear. Amy and Bernadette, however, appear in the title sequence.
- Recurring characters often and frequently appear from time to time during the series' run.
- The series features a large number of guest appearances, some of whom are celebrities appearing as themselves. The screen time of the guests is very low.
The following table shows a list of main and recurring characters and illustrates a breakdown of their appearance throughout by season.
Original main characters
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. Over the next two years they talk of marriage and each have unsuccessful proposals until the end of season seven when they become engaged. 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.
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 personality disorder, performing specific activities on specific days and specific 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 and by season 7 they having started kissing each other. Previous to this, he has also exhibited some affinities with Leonard's equally unemotional mother.
Penny (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 romantic 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 at the end of season five. After several unsuccessful proposals from both sides, Penny realizes that her happiness is derived from her relationship with Leonard and they become engaged. She has a tense relationship with Sheldon, whose nerdy and obstinate personality often exasperates 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 dealer. Cuoco began being credited as Kaley Cuoco-Sweeting, starting with the season seven episode, "The Convention Conundrum".
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.[episode needed] 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.[episode needed] 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. In season 6, he finally leaves his mother's house and moves into Bernadette apartment.
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, Amy and Bernadette are 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. In season 7, Raj begins to interact with women ending the season with a red-headed girlfriend named Emily.
Additional main characters
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. Her first appearance was in the third episode of season one. 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. After Penny broke up with Leonard, she got intoxicated, had intercourse with him, then pushed him away. Distraught, Leonard asked for intercourse with Leslie. Leslie responded, "Let me think about it," before slamming the door on him.
Dr.[a] Bernadette Maryann Rostenkowski-Wolowitz (Melissa Rauch): (has appeared in 101 episodes total, 96 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 Coating Corollary". A recurring joke in the series is in reference to Bernadette and her lab team handling dangerous or infectious specimens, leading to accidental by-products or exposure to diseases, in some cases resulting in Bernadette ending up in quarantine. Instances include her trying to remember whether she washed her hands while she worked with penicillin-resistant gonorrhea or creating a cold medicine that may cause acidic tears. She is of Polish origin and Catholic upbringing, and is frequently seen wearing a cross necklace. She is generally a friendly and good-natured individual, quickly making friends with Penny and Amy, as well as the rest of the gang, but occasionally shows signs of mania, e.g. when she got into a fight with Amy over a parking space Sheldon and Howard were fighting over, and when she explains her interest in microbiology as being because she feels like a God to the bacteria she is studying. She has complete influence over both her father and her husband as she freely overrules her father without being contested and directly supervises Howard's expenditure by giving him allowance money. On one occasion, she was also able to control Sheldon, putting it down to knowing how to deal with stubborn children.
Penny first introduced Bernadette to Howard on Leonard's half-willing request. During the first date, Bernadette and Howard do not find any common field of interest until they find out that they both have domineering mothers. After three dates, Bernadette blindsides Howard by declaring that three dates is the threshold for deciding whether they want a long term relationship. She is not impressed by Howard's failure to reply readily and is even more repulsed by Howard's subsequent impulsive proposes to her. However, when Howard sings a heartfelt song for her at the Cheesecake Factory, she declares that it is the most romantic thing anyone has ever done for her. A lengthy offscreen breakup occurs when she catches Howard engage in cybersex. After a brief apology from Howard, she consents to restarting (as opposed to resuming) their relationship. In the season 4 finale, she obtains her doctorate and is subsequently hired by a pharmaceutical company with a high salary. While preparing for their wedding, Bernadette is shocked and repulsed when stories of secret sexual escapades from his past are released, although once again, the apology and reconciliation occurs quickly in the same episode. They get married the day before he leaves for his upcoming mission at Houston. During season 6 and 7, the newlyweds battle issues involving Howard's difficulty in readjusting to being back on Earth, the struggle to keep a healthy relationship with Howard's mother, and arguments over expenditure. Despite numerous problems and squabbles, Howard and Bernadette exhibit the only steady relationships on the series.
Amy Farrah Fowler
Dr. Amy Farrah Fowler (Mayim Bialik) (has appeared in 95 episodes total, 89 credited as main cast) is a neuroscientist (which corresponds to Bialik's real-life Ph.D.), and Sheldon's love interest in the series. She has a Ph.D. in neurobiology, with a research focus on addiction in primates and invertebrates, occasionally mentioning such experiments as getting a capuchin monkey addicted to cigarettes or starfish addicted to cocaine. Raj and Howard found Amy through an online dating site after secretly setting up an account using Sheldon's name and information. The site matches her to Sheldon, and the two share many similar traits. Once she and Sheldon meet, she becomes, as Sheldon puts it, a girl who is his friend, but not his "girlfriend." They briefly ended their friendship when they got into an argument over whose field of study was superior. The two initially communicate via computer, but at the encouragement of the group, she starts hanging out with the gang in person. Early on, Amy is, essentially, a female counterpart to Sheldon. During this time, she is almost coldly rational while displaying little emotion, is awkward in social situations ranging from endearing to embarrassing, is sometimes condescending towards those of lesser scientific knowledge and has little or no desire for physical intimacy. In Season Five, after Amy went out on a date with comic book store owner Stuart, Sheldon decided to solidify their relationship as boyfriend/girlfriend with a 31-page "Relationship Agreement". Amy began a campaign in "The Launch Acceleration" to increase Sheldon's feelings for her by becoming more involved in his interests like video games and Star Trek, and treating him as his mother had. During Howard and Bernadette's wedding ceremony, Amy is disappointed when Sheldon says that he hopes that the two of them are as happy together as he is alone. Later as Howard is launched into space, Amy is surprised when Sheldon spontaneously takes her hand for comfort. Despite her best efforts, however, he repeatedly resists all of her attempts at persuading him to engage in physical intimacy though they are regularly holding hands at Amy's insistence at the beginning of season 6. By mid-season when Sheldon was caring for her when she had the flu, Sheldon has some intimate views of Amy pushing him further toward a normal relationship with her. She has also provided Sheldon with consoling hugs and was slapped on the rear by an intoxicated Sheldon, telling everyone that she is a great gal. Amy tried to move into his apartment when Leonard temporarily vacated it. After being prodded by Barry Kripke about his girlfriend, he lied that they were having sex, though he admitted to Penny that it might really happen between him and Amy and later admitted it to Amy while also engaging in Dungeons and Dragons' intercourse game play. Nevertheless, her frustration is frequently played for laughs from that point onward. In the Season 7 episode "The Locomotive Manipulation", Sheldon sarcastically says he will give Amy the romance she wants, then he passionately kisses Amy on the lips for the first time and enjoys it.
While early on Amy was ambivalent and often condescending towards Penny and Bernadette, she later spends more time with them even at the expense of her time with Sheldon. As her appearances have progressed, she has shed her strident, aloof personality for a stereotypically feminine and social one, although she retains some social awkwardness. Her feelings for Sheldon have also grown considerably over time and considers him to be ideal in almost every way, though she sometimes becomes as annoyed and frustrated by Sheldon's quirks as his other friends do. Amy also intensely wants her relationship with Sheldon to progress to include sexual intimacy, a drastic departure from her early days as a member of her circle of friends. She has come to consider Penny a very close friend, sometimes referring to her as her "bestie," and, on another occasion, admitting her entire social life revolves around her. Penny herself is fond of Amy, on one occasion making an effort to salvage their friendship after she accidentally hurt her feelings. To her dismay, however, Amy often fails to grasp the concept of "girl talk," by talking about feminine hygiene and anatomy when in her presence and at times being brutally honest. Also, Amy often demonstrates an infatuation towards her, and occasionally Bernadette, to whom she is still rather condescending though still considers a close friend. These including making inappropriate comments about Penny's body and Bernadette's personality. After attending a science convention with Bernadette in "The Hofstadter Insufficiency", Bernadette and Amy found common interests and became better friends. When she feels that Leonard is interested in her, she admits to Penny that she has a better shot getting her into bed than Leonard. In episode 8 of the fifth season, she suggests that Bernadette's bridal shower should consist of naked bridesmaids washing each other, and she proposes that the bachelorette party consist of a Native American sweat lodge and women dancing around painting fertility symbols on the bride's naked body. Her more arrogant side is shown in "The Pulled Groin Extrapolation", where she is convinced that Leonard has fallen for her after he accompanies her to a friend's wedding and gives her a chaste kiss on the cheek, even though he has no such feelings. In "The Benefactor Factor", it is revealed that she is technically engaged to Saudi Arabian Prince Faisal who resides in Riyadh, who is the source of much of her lab's funding. Amy can also play the harp. In "The Scavenger Vortex," it is suggested that she attended Harvard University.
Stuart Bloom (Kevin Sussman) (appeared in 33 episodes total, seven credited as main cast) Stuart runs The Comic Center of Pasadena, the comic book store that the guys patronize. Stuart is characterized by his low self-esteem and loneliness, which result in pathetic attempts to engage with women and win favor with the main cast. This is despite owning his own (albeit troubled) business, and being a talented portraiture artist who attended the Rhode Island School of Design.
During Stuart's first appearance, the guys brought Penny to the store and he managed to ask her on a date. The date went fine until Stuart was dragged into discussing comic books by Sheldon, leaving Penny bored. On a second date with Penny, Stuart asked for Leonard's advice, but feeling threatened, Leonard ultimately gave him bad advice. The date went fine, but when Penny was getting romantic with Stuart she mistakenly called him "Leonard", leaving him devastated. He also briefly went on a date with Amy in season 5; although Sheldon interrupted the date to solidify his relationship with Amy. Stuart was the partner of Wil Wheaton in a trading card game tournament in which they defeated the team of Raj and Sheldon. As Stuart runs a comic book store, he has an almost encyclopedic knowledge of comic books and superheroes. In the Season 4 episode "The Toast Derivation", he mentions that he is in financial trouble and that the comic book store is now also his home. In "The Justice League Recombination", he states that he works 70 hours and clears an average of $1.65 per hour after expenses, so his income per week would be $115.50. At Howard's bachelor party during the "The Stag Convergence" episode, Stuart uses his toasting turn to tell Howard how lucky he is by contrast to Stuart's own existence. In the Season 6 episode "The Bakersfield Expedition," Penny asks Stuart for advice about comics, and he sullenly answers, "Don't own a store that sells them." During "The Decoupling Fluctuation", Stuart becomes close friends with Raj and starts hanging out with the gang as a replacement for Howard while Howard is in space. Before accepting this, Sheldon quizzed Stuart as to where he went to school (Stuart has an art degree). Sheldon concedes to allow Stuart to be in the group, calling him "fake-Wolowitz" and equating his past career choice in art to Howard's as an aerospace engineer as "equally ridiculous". When Howard returns from space Sheldon wants to dismiss Stuart from the group but Raj objects. Leonard tie-breaks on the basis that they are receiving a 20% discount in Stuart's store. Sheldon relents after Stuart offers to go as high as 30%. Initially, Sheldon had stipulated that Stuart must act like Howard while in the gang's presence.
The following list is sorted in alphabetic order of first names.
Alex Jensen (Margo Harshman): An attractive Caltech graduate student who appears in season six. She is hired by Sheldon to review his kindergarten and elementary school notebooks for any possible Nobel Prize winning research and attend to the tasks that Sheldon perceives a waste of his own valuable time. Amy is at first jealous until she sees Alex instead flirting with an unresponsive Leonard. After repeated flirts by Alex, Leonard finally realizes that Alex is making advances toward him. While proclaiming his loyalty to Penny, Leonard is flattered. Sheldon interferes (with the perceived intention of mitigating a situation that needed none) by lecturing Alex, but only succeeds in insulting her. After Alex files a sexual harassment complaint, Sheldon is forced to apologize and is ordered take a university-mandated online sexual harassment course. Because Sheldon considers his own time is too valuable to waste on it, Sheldon asks Alex to take the course instead.
Alex scores some points with Sheldon after he sends her out to buy Amy a Valentine's Day gift, and Sheldon likes it so much that he keeps it for himself.
Barry Kripke, Ph.D. (John Ross Bowie): A coworker of Leonard and Sheldon's who frequently clashes with them. He works in plasma physics. Kripke has a case of rhotacism in which he pronounces the letters "R" and "L" as "W" in much the same way as Elmer Fudd from Looney Tunes and Gilda Radner in her "Baba Wawa" sketches. Until Season 7, it was never clarified he was aware of his impediment, however in "The Discovery Dissipation", when Sheldon mocks his impediment, Barry appears visibly hurt and tells Sheldon he has no control over it. In his first appearance, he pits his robot, the Kripke Krippler, against the men's robot, M.O.N.T.E., in an unofficial robot fight. On another episode, Sheldon attempts to befriend Kripke in order to gain access to an open science grid computer to carry out research, but it turns out to be futile, as Kripke has no control over the computer's usage time. Kripke continues his antagonism towards Sheldon, when he pulls a prank on Sheldon when the latter is a guest on NPR's Science Friday. Sheldon tries to befriend Kripke another time when he is feeling excluded by his friends, but Barry connects more with the others in Sheldon's new proposed group. Kripke purchases an iPhone with voice recognition technology, but due to his rhotacism, the device is incapable of understanding his verbal "wequests", prompting him to deride it as ineffective. In Season 5's "The Rothman Disintegration", Kripke and Sheldon battle over a retired professor's office. At Howard's bachelor party during the "The Stag Convergence" episode, Kripke uses his turn toasting to complain that there are no strippers at the party. In the Season 6 episode "The Cooper/Kripke Inversion", Kripke and Sheldon are forced to work together on a proposal involving fusion reactors, which involves an exchange of work. Sheldon is shocked to discover that Kripke's work is more advanced than his own, and he tearfully admits as much to Amy. Kripke assumes that Sheldon is in a sexual relationship with Amy, and that has led to his work quality declining, and Sheldon does not deny it (although this appears to be just a convenient excuse since his work is inferior to Kripke's). Kripke likely holds a doctorate, as he is seen applying for tenure at the university in "The Tenure Turbulence."
Dr. Beverly Hofstadter (Christine Baranski): Leonard's overly analytical mother, Beverly is a neuroscientist as well as a psychiatrist. She is Sheldon's female equivalent regarding neurotically strict speech patterns, lack of social conventions, and attention to detail. The two of them share an odd non-romantic attraction to each other, which culminates in her kissing him after becoming intoxicated. She reveals in one episode that she and Leonard's father "are getting a divorce". She had frequently implied that the two have not had "coitus" since Leonard was conceived. One of her famous books is "Needy Baby, Greedy Baby," in which she describes an infant's (aka Leonard's)unrealistic nurturing expectations. Sheldon often refers to the book when frustrated with Leonard's attempt to obtain some of his personal needs in their relationship. In one episode she also relates to Leonard that his vague memory of living with an ape and learning sign language was part of an experiment she conducted during Leonard's early years. Beverly reunites Leonard with his long-lost ape friend after Leonard's insistence that she do so. Leonard sees his mother as cold and un-nurturing, even telling the group that one time he made a hugging machine just to get hugs. The lack of Beverly's maternal feelings and actions toward Leonard have led to his being determined "King of the Foreplay" because of his obsessive need to please.
Beverly diagnosed Raj with selective mutism and considers Raj and Howard's relationship to be an "ersatz homosexual marriage". Beverly mentions that Leonard's brother and sister are more successful in their respective fields than he is. Ironically, as displayed in "The Maternal Congruence" episode, Sheldon is closer to Beverly than her own son is. In both 2009 and 2010, Baranski was nominated for an Emmy Award for Outstanding Guest Actress in a Comedy Series for this role. She returns via Skype for the season 5 premiere, and in the season 7 episodes "The Raiders Minimization" and "The Status Quo Combustion".
Dr. Eric Gablehauser
Dr. Eric Gablehauser (Mark Harelik): The head of the Physics Department, Dr. Gablehauser is the group's boss at the university. In his first appearance, he fired Sheldon after Sheldon insulted his intelligence. Eventually, Sheldon was rehired because Gablehauser became romantically interested in Mary Cooper, Sheldon's mother. Dr. Gablehauser was also responsible for introducing child genius Dennis Kim to the university and for hosting the Physics Bowl.
Dr. and Mrs. Koothrappali
Dr. V. M. Koothrappali (Brian George) and Mrs. Koothrappali (Alice Amter): Raj's parents in India, they communicate with their son via video chat and constantly try to arrange dates for him. They want their son to marry a woman of Indian descent, and give them grandchildren. Mrs. Koothrappali is especially worried that, despite Raj being old enough to marry, the closest they have to a daughter-in-law is "that little Jewish boy Howard". Although in many episodes Raj mentions that he grew up in poverty, his friends remind him of the contrary by pointing out that Dr. Koothrappali is a gynaecologist, drives a Bentley and employs servants, for which Raj replies that the Bentley is leased and that some of the servants are children. The Koothrappalis enjoy Doogie Howser reruns, which are apparently new to India. Other than Raj, they also maintain contact with Priya Koothrappali via video chat whenever she is out of India. They also had some anger towards Leonard when it became apparent that he was dating Priya without their knowledge. According to Sheldon, they are Richie Rich rich.
Emily Sweeney (Laura Spencer): A dermatologist who initially contacts Raj through an online dating site. The reluctant Raj has Amy contact her as his wingman instead. Amy and Emily exchange emails and find they have a lot in common. They both went to Harvard, are doctors, and like crocheting and Chaucer. Emily doesn't like Raj's inability to correspond with her directly, and when Amy and Emily meet to have coffee, Raj barges in to show that he is not a passive guy. Emily calls him a weird guy with no boundaries and leaves. She also ditches Amy for their next get together. In "The Indecision Amalgamation", Raj meets Emily again and apologizes. She gives him another chance and agrees to go out to dinner with him. Later on, Raj finds out that his ex-girlfriend Lucy wants to see him again and he finds himself dating two women, although this does not bother Emily. In "The Relationship Diremption", Raj and Emily have dinner with Howard and Bernadette. Howard figures they should do it quickly because Raj is bound to mess up his relationship very quickly. Upon meeting Emily, Howard recognizes her because he had a blind date with Emily sometime near 2009 before he met Bernadette. He had a sick stomach, had to use the bathroom and clogged the toilet. Since he was too embarrassed to tell her, he escaped through the bathroom window. Emily reveals that she and her friends refer to Howard as "Clogzilla". In "The Anything Can Happen Recurrence", Raj and Howard watch the gore-fest "House of 1000 Corpses" because Emily wants to watch it with Raj. They are both turned off and wonder about someone who likes this type of movie. On their date, Raj tells Emily how he feels about it and she also wonders about someone who likes this film. She also admits that it turns her on, so Raj immediately starts it so they can watch it. In "The Gorilla Dissolution", Raj and Sheldon find Emily at the movies with another guy. Later she visits him to talk and reveals that the guy was her tattoo artist who had been asking her out for weeks and she did so just to end the obligation. She mentions a tattoo on her shoulder, one that is not on her shoulder and one that is REALLY not on her shoulder. Emily then spends the night and in the next episode, Raj reveals that he and Emily are now exclusive. Raj and Emily are still dating in season 8, and she is introduced to Leonard and Penny, the latter to which she is initially cold to. Emily later reveals that she is uncomfortable with the fact that Raj and Penny hooked up in "The Roommate Transmogrification". Emily and Penny later sit down to settle their differences; however after the meeting both women state that they hate one another.
Janine Davis (Regina King): A human resources representative working at the university who handled a sexual harassment complaint against Sheldon. Sheldon, in his attempt at defense, rats out "worse behavior" by Raj, Howard, and Leonard, prompting Mrs. Davis to summon them to her office as well. In a later episode, Mrs. Davis serves on the tenure committee that is considering Raj, Sheldon, Leonard and Kripke for a vacant tenured position, causing each of them to try to "butter up" Mrs. Davis. In season 7's "The Hofstadter Insufficiency", Mrs. Davis is revealed to be recently divorced, and Raj attempts to strike up a conversation with her at a university mixer. She also appears in "The Junior Professor Solution".
Lucy (Kate Micucci): A woman who shows up at the party at the comic book store on Valentine's Day for people who had no dates. She and Raj hook up and subsequently start dating. She has social anxiety issues, which allows her and Raj to connect. On their date, she text messages with Raj and, at the end, she offers to kiss him, but chickens out at the last second. Raj and Lucy make up at the end of the episode and continue to date. In the sixth season finale, Raj and Lucy start to get closer and Raj tries to introduce her to his friends. Lucy feels too pressured and breaks up with Raj in a text message at the end of the episode. She returns in the season 7 episode "The Itchy Brain Simulation" to apologize to Raj for breaking up with him via email. This leads Raj to believe the two of them will get back together, but Lucy tells him she is with someone else.
Mary Cooper (Laurie Metcalf): A devout fundamentalist Christian from Texas, Mary is Sheldon's mother. She has two other children besides Sheldon; Sheldon's twin sister, Missy and his brother George, who is shown via a family tree in "The Cruciferous Vegetable Amplification" to be three years older than Sheldon and Missy. To Mary's relief, her other children do not share Sheldon's hyper-intelligence, once commenting to Leonard "I thank the good Lord my other kids are as dumb as soup". She appeared in the fourth episode of the first season, the season three premiere, the third episode of season four, the sixth episode of season five and the eighteenth episode of season seven. Mary herself is not intellectual but is quite wise, though she is prone to making insensitive comments such calling Japanese "kung fu letters" at sushi restaurant, or calling Native Americans "our Indians". Despite her extreme religious views, she is tolerant of other faiths, as evidenced by her serving Raj a dish of chicken after making sure it was not something Indians considered "magical". She also struggles to follow her beliefs sometimes, shown through her affair with another churchgoer in "The Mommy Observation". She is a loving mother and the only one who has ever been able to control Sheldon, with Leonard describing her as Sheldon's "Kryptonite" to Penny. When Penny and Sheldon engaged in a fierce dispute, Penny called for Mary's help, who subsequently called and scolded Sheldon about his actions. Leonard wishes his mother was as loving as Sheldon's mother, although Sheldon himself appears at best ambivalent about her parenting. It is once mentioned by Sheldon that Mary once hit him with a Bible because he refused to eat his Brussels sprouts. She apparently thought something was wrong with her son while he was growing up, as Sheldon will often remark after someone calls him crazy, "I'm not crazy; my mother had me tested!" Though Mary Cooper confirms this, she wishes that she had taken him to Houston for further testing.
Mike Rostenkowski (Casey Sander), first introduced in season 5, is the father of Bernadette. Mr. Rostenkowski is a hardened police officer, who has a rough and rude personality, and often bullies others. He admitted to Howard that he does not like him, but is impressed with him being an astronaut. He appears to have a soft spot for Bernadette, calling her his "little girl." Before he was first seen, Bernadette warned Howard not to mention Jimmy Carter, gardeners, foreigners, homosexuals, Sean Penn, Vatican II, organic food, gun control, recycling, or Howard's Jewish heritage, indicating that he is far-right-wing. Whilst initially cold to Howard, his respect for Howard grew, however, when he learned Howard had been selected to become an astronaut. When Howard told him of his terror of going to space, Mr. Rostenkowski said "It's gonna be okay, son. A pretty girl like Bernadette... She'll find a new guy." In "The Fish Guts Displacement", Howard and Mike get pushed into a fishing weekend by their spouses and it turns out neither of them want to go. Mike suggests that they go to a casino to shoot craps. They bond somewhat and he tells Howard to call him Mike and no longer "Sir". In "The Thanksgiving Decoupling," his wife is out of town and Bernadette gets him to come to Howard's mother's house for Thanksgiving dinner though he would rather watch football at home. Since Sheldon knew football thanks to his father, Mike and Sheldon bond and get drunk together. Mike later tells Howard that he isn't "all that bad", however he retorts that he is drunk. In "The Table Polarization," he, Bernadette, Raj and Mike Massimino (via web chat) perform an intervention on Howard's decision to go back to space (he had to be prodded by Bernadette to agree about loving him). He mentioned that Howard asked him to shoot him in the foot, at which Howard insisted was a joke.
Priya Koothrappali (Aarti Mann): Raj's younger sister, introduced in the fourth season. Having graduated at the top of her class at Cambridge, she is one of the lead attorneys at India's biggest car company. It is disclosed upon her first appearance in "The Irish Pub Formulation" episode that she and Leonard had a relationship five years earlier (without her parents' or Raj's knowledge) when she was in town, and that Leonard had been much more invested in the relationship than she. Leonard even offered to relocate to Delhi to be with her. He tries to keep their relationship a secret from the guys, but Sheldon discovers Priya in their apartment. Leonard eventually reveals to the rest of the guys that he has spent the night with Priya, as he is unable to bear the burden of keeping the secret. Priya returns to Los Angeles for business in "The Cohabitation Formulation" and she and Leonard decide to try and have a real relationship, over the protests of Raj. It upsets Raj to know that his sister is having sex with one of his best friends (sometimes in Raj's bed). Priya soon becomes jealous of Penny and asks Leonard to stop spending time with her, but Leonard is unable to do so. Priya contests Sheldon's roommate agreement with Leonard, employing her legal background to deny Sheldon power over Leonard, but Sheldon drafts a new agreement. Sheldon then blackmails Leonard into signing it by threatening to tell Priya's parents she is dating Leonard, which she cannot bear because they want her to date an Indian (although her father would accept her dating Howard due to his belief that Jews are financially savvy and do not drink much). In the fourth season finale, it is revealed she is moving back to India and has not told Leonard, which Leonard interprets as the end of their relationship, leading him to expose their secret relationship to her parents. During Season 5, although they are separated, with Priya moving back a month earlier than expected, they nonetheless remain in-touch via webcam, having a cyber-dinner date/breakfast date. At Howard's suggestion, Leonard and Priya also attempt to simulate intercourse via webcam, but when it comes time for her to remove her clothing, Leonard's screen freezes up because of exceeding the bandwidth. Leonard later manages to get cue cards to help himself with a seduction speech to Priya, but while delivering it to her, he inadvertently reveals to her parents that they are cyber-dating (they were in the same room as she when he called), with them acidly asking for him to continue with the speech. After Leonard tells Priya about his attraction to a comic book enthusiast named Alice, Priya admits to cheating on him with her former boyfriend, which visibly upsets Leonard. She claims that it is not a competition, to which he replies that it is and that she won. Then he switches off his laptop. In the next episode, Leonard refers to himself as single, indicating he and Priya have broken up as a result of their last conversation.
Dr. Stephanie Barnett, MD (Sara Rue): A doctor and highly distinguished surgical resident at Fremont Memorial, Stephanie is picked up in a bar by Howard but when his plan to let her drive the Mars rover fails, she leaves Howard's office with Leonard and the two immediately show an attraction to each other. Sheldon begins meddling in Stephanie and Leonard's new relationship in an effort to strengthen it, since in his eyes, Stephanie is the only "tolerable" mate Leonard has had. After several weeks of dating, Stephanie officially begins living with Leonard in his and Sheldon's apartment. However, after much hesitation, Leonard tells her to move out because he is uncomfortable with the pace of the relationship. They are not seen breaking up on camera. Series co-creator Bill Prady said of the relationship: "Stephanie was a chance for Leonard to learn that just because someone loves you, doesn't mean you'll love them back". Stephanie did her medical internship at Lawrence Memorial in Galveston, Texas, which is where Sheldon was born.
Wil Wheaton (a fictionalized version of the real actor of that name): In the season three episode "The Creepy Candy Coating Corollary", Sheldon enters a trading card game tournament (Mystic Warlords of Ka'a) to confront Wil Wheaton over an incident that occurred in 1995 when Sheldon was devastated because Wheaton (Wesley Crusher in Star Trek: The Next Generation) failed to show up at a fan convention that Sheldon took a 10-hour bus ride to attend (in which he had to "twice violate his personal rule of no relief on a moving vehicle"). In the final match, Sheldon is about to defeat his hated rival, but Wheaton tells Sheldon that the reason he missed the convention was because his grandmother had died. In sympathy, Sheldon deliberately messes up his next move in order to benefit Wheaton. Wheaton reveals that he lied about his grandmother, then wins the game by taking advantage of the opening Sheldon left him. Wil Wheaton makes a second appearance in the episode "The Wheaton Recurrence", where he uses gamesmanship again, breaking up Leonard and Penny's relationship in order to win a bowling competition against the main characters. In "The 21-Second Excitation", Wheaton appears at a screening of Raiders of the Lost Ark and uses his celebrity status to go to the front of a long line. This antagonizes Sheldon, who derides him as the "Jar Jar Binks of the Star Trek universe." Wheaton and his entourage effectively prevent Sheldon and the guys from attending the screening when the last seat in the theater goes to the person directly in front of them in line. Ultimately, Sheldon steals the prints of the film and Wheaton leads a mob of angry Raiders fans after Sheldon. In the season five episode "The Russian Rocket Reaction", Wheaton appears to be genuinely sorry for his past actions and gives Sheldon a signed Wesley Crusher action figure as a way of thanking Sheldon for being a fan. His gesture is met with a renunciation of his "mortal enemy" status, and a hug from Sheldon. With Wheaton, LeVar Burton, Leonard Nimoy, Brent Spiner and George Takei also having appeared on the show, Star Trek is the most represented franchise on the show in terms of guest appearances. At Howard's bachelor party during the "The Stag Convergence" episode, Wil films the toasts and uploads them to the Internet, getting Howard and Raj in trouble with Bernadette and showing that he has not lost all of his "evil" quirks. In the season six episode "The Habitation Configuration", Wheaton appears in a Star Trek-themed episode of Sheldon's webseries Fun with Flags, and insults Sheldon's girlfriend (and the webisode's director), Amy. After he ditches Amy to hang out with Wheaton, Amy gets angry at Sheldon; he later unknowingly becomes inebriated and tries to start a fistfight with Wheaton, demanding an apology.
Mrs. Debbie Wolowitz (voiced by Carol Ann Susi): Howard's controlling, belittling Jewish mother. The character is not shown on-screen with the exception of one episode in season 6 in which her body, but not face is briefly shown and also as a skeleton in season 7. Mrs. Wolowitz's raspy voice is heard usually in scenes at her house, which she shared with Howard until his marriage. She talks to Howard always by yelling at him from another room, which results in awkward conversations with Howard yelling back at her. In an early episode, when the guys hear her yelling in a masculine voice, they ask Howard if that was his father, to which Howard replies "If she grows any more hair on her face, yes".
She is also described as being enormously obese (especially in the arms), and wearing a wig and painted-on eyebrows. Mrs. Wolowitz seems to be oblivious about Howard's work as an engineer and treats him like he is still a child. She frequently refers to Leonard, Sheldon, and Raj as Howard's "little friends" (as in, "I made some cookies and Hawaiian Punch for you and your little friends!") and often refers to Caltech as a "school". Howard often makes references to his mother as being a "crazy old lady", but deep down, he is deeply attached to his mother and quite happy to be treated like a child. However, in one episode, Howard attempts to move out after a fight with his mother, but has serious delusions that she is trying to force him to stay, when in actuality, she is urging him to move out, which leads to him staying. In the penultimate episode of season 4, she wants to "play doctor" with Raj when he asks to sleep over.
When Howard reveals that he has proposed to Bernadette and she has accepted, she collapses, causing Howard to panic (and dislocate his shoulder while trying to barge into the bathroom to help her). The timing leads him to believe that she may not like Bernadette (who is Catholic) and has suffered a heart attack from the shock of the news. In actuality, her fainting was due to food poisoning from the food she ate while meeting Bernadette, and was completely unrelated to Howard's news. She has graciously accepted Bernadette as her future daughter-in-law and loves that she is a doctor. She attended Howard and Bernadette's wedding on Leonard/Sheldon/Penny's apartment building roof and can be seen in the satellite picture of the event. The episode "The Spoiler Alert Segmentation" is a major episode in Mrs. Wolowitz's character as she appears on screen for the first time; first walking across the kitchen through the kitchen doors, and then her hands are seen pulling Raj back into the house. Her face is not seen at all, but her appearances in the kitchen scene make her out to be an extremely obese woman.
Zack Johnson (Brian Thomas Smith): A dim-witted, but friendly beefcake-type whom Penny dates after her second break-up with Leonard. Leonard invites Penny and Zack up to the roof to watch his experiment of bouncing laser beams off the moon; Zack misunderstands what is happening. Later, he and Penny go out on a date, but she is so put off at how stupid he is that she runs back to Leonard to have sex, saying that Leonard has ruined her ability to date stupid men. In a later episode, Zack runs into Penny, Bernadette, and Amy at a restaurant, and Amy becomes physically attracted to him. Unlike Penny's other boyfriends, he considers Leonard, Howard, Sheldon, and Raj (whom he calls "the science guys") to be "cool" and makes a genuine effort to get to know them, considering them to be his friends. After accompanying them on a trip to the comic book store (where he and Raj bond over a mutual fondness for Archie comics), he enters a New Year's Eve costume party with them, portraying Superman in their version of the Justice League. He works as the menu designer for restaurants that are owned by or which have hired his father's company to design their menus. In "The Toast Derivation", Sheldon invites him over for a party, where he bonds with Barry Kripke and Stuart as well. It is revealed in season 7's "The Thanksgiving Decoupling" that he was unknowingly married to Penny for three years, after they got intoxicated and attended a wedding chapel in Las Vegas.
These characters appear in fewer episodes, most in just one. The list is in alphabetic order by first name.
Appearing in multiple episodes
- Althea (Vernee Watson) A character who makes an appearance in the pilot episode as an attendant at a sperm bank, and then makes three appearances as an emergency room nurse in "The Peanut Reaction" episode (Season 1) and "The Robotic Manipulation" episode (Season 4), and as a ward nurse in "The Werewolf Transformation" (Season 5). The name of the character is never used on the show, but is included on her nametag and in the credits. She is also the only character besides Leonard and Sheldon to be carried over from the original unaired pilot.
- Arthur Jeffries, aka Professor Proton (Bob Newhart): The star of the science show that Sheldon and Leonard watched as children. After the show was cancelled, Jeffries was not taken seriously as a scientist and resorted to doing children's parties as his persona. Sheldon hires him to do a private party for Leonard and himself (and Penny), and he ends up having a heart attack after climbing the apartment stairs with his equipment. He asks Sheldon to take his place at a party for a Korean family, which Sheldon agrees to do as Professor Proton, Jr. Arthur returns again, this time in a drugstore, where he runs into Leonard, Sheldon, and Amy; and is disappointed that Penny is not with them. In his third appearance, Leonard tells Sheldon that Arthur has died, which Sheldon immediately pretends like he doesn't care. Arthur appears to Sheldon in a dream, where Sheldon compares him to Obi-Wan Kenobi, and is immediately dressed in Jedi robes and appears as a Force ghost. Arthur tells Sheldon later to appreciate everything in life, and never take it for granted.
- Bert (Brian Posehn): A socially awkward geologist. His first appearance was in Season 6, Episode 18, "The Contractual Obligation Implementation", when he meets Raj and Lucy in the library during their date. Later in Season 7, Episode 13, "The Occupation Recalibration", he is found having a crush on Amy and tries to ask her out on a date to a Geology Rock Show.
- Captain Sweatpants (Ian Scott Rudolph) and Lonely Larry (Owen Thayer): Two men that are sometimes seen at the guys' favorite comic book store. Captain Sweatpants is a middle-aged bald man who wears grey sweatpants and a City of Heroes T-shirt. Lonely Larry wears a brown suit and is extremely thin. They are also friends with Wil Wheaton. Both attend Howard's bachelor party.
- Cheryl (Erin Allin O'Reilly): Apparently a friend of one of Penny's friends (because it is subtly suggested she may not know many of the people at the party), who attends Penny's Halloween party in Season 1, Episode 6, "The Middle Earth Paradigm". Cheryl is the very talkative, short-haired brunette dressed as a ladybug, who hits it off with Raj. She is not identified within the episode, but is listed in the credits. She appears again as a Cheesecake Factory waitress in "The Pancake Batter Anomaly".
- Dale (Josh Brener): Dale works as a replacement for Stuart at the comic book store when he went on a date with Amy "The Flaming Spittoon Acquisition", and also appears in "The Tangible Affection Proof" at Stuart's Valentine's Day party.
- Dimitri Rezinov (Pasha Lychnikoff): A Russian cosmonaut who is Howard Wolowitz's colleague on his Soyuz mission to the International space station.
- Kurt (Brian Patrick Wade): A tall, intimidating bodybuilder, Kurt is Penny's ex-boyfriend at the beginning of the series. In the pilot-episode, Leonard and Sheldon went to his apartment and tried to retrieve Penny's television set from him, but they did not succeed and Kurt apparently found them so irritating that they returned home without pants. Penny left him because he cheated on her, but he was still invited to her Halloween party, for which he dresses up as a caveman. In season 2, episode 14, Penny experiences financial difficulties, Leonard and the guys confront Kurt over $1,800 in legal fine money Penny had lent him. Immediately refusing, Kurt shortly thereafter pays Penny and the two have dinner, but is never seen again.
- President Siebert (Joshua Malina): The president of the California Institute of Technology; he is married and has a teenage daughter. Siebert sends Sheldon on an expedition to the North Pole at the end of Season 2. In Season 4, he organizes a get-together with wealthy donors and faculty in order to garner funds for the university's programs. He urges the guys to make an appearance to schmooze the donors so that they will give to their projects. Seeing Sheldon's behavior toward the donors, he asks that he not appear again. A recurring gag is that President Siebert bumps into Sheldon when he is using the urinal.
- Mike Rostenkowski (Casey Sander): Bernadette's father, a retired police officer who has a rough and abrasive personality. He is not very accepting of Howard until he learns that Howard will be going into space as an astronaut. After an aborted weekend fishing trip, Howard and his father-in-law bond over learning to play craps at an Indian casino.
- Mrs. Rostenkowski (Meagen Fay) : Bernadette's mother. She is a woman of few words, like her husband. She displays a lot of the same characteristics of her daughter. When Howard first met Bernadette, they bonded over the similar personalities of their controlling mothers.
- Todd Zarnecki (Christopher Douglas Reed): Appears in "The Zarnecki Incursion" episode as a hacker who "steals" Sheldon's possessions in the World of Warcraft online game. Being physically much larger and more intimidating than the four main characters, they back down from confronting him. Penny picks them up, takes them back to Todd's house and sets Todd straight with a swift kick to the groin. He also shows up at Howard's bachelor party (as an unnamed attendee), and in the Season 6 episode "The Tangible Affection Proof", he is in attendance at Stuart's party on Valentine's Day.
Appearing in one episode only
- Abby (Danica McKellar) and Martha (Jen Drohan): With Leonard and Howard busy on a double date with Penny and Bernadette, Raj and Sheldon attend a university mixer where they meet Abby and Martha. Abby takes a liking to Raj, while Martha surprisingly seems to connect with Sheldon. While Raj and Abby end up kissing, Sheldon completely ignores Martha, who even tries to go to bed with him. Like series regular Mayim Bialik, McKellar exists within the Big Bang Theory universe independently of Abby, having been mentioned alongside Bialik in ep. 1.13, "The Bat Jar Conjecture". Like Bialik, McKellar is a scientist in real life.
- Alice (Courtney Ford): An attractive comic book enthusiast who meets Leonard at the comic book store, and takes him to her apartment and tries to hook up with him. This date occurs during the period when Leonard is having a long distance relationship with Priya. Leonard initially gives in to temptation, but at the last minute pulls away. He tells Alice about Priya, that his super power is being a good guy, and then gets thrown out of her apartment. The next time he communicates, via the webcam, with Priya, he confesses his weakness. To his surprise, Priya has no problem with it. Upon questioning, Priya reveals that she has not been faithful to Leonard. They then break up.
- Alicia (Valerie Azlynn): A young woman who moves into an apartment above Leonard and Sheldon in the "Dead Hooker Juxtaposition". Penny displays a fit of jealousy at this turn of events, thinking that Alicia is supplanting herself in the boys' attention. Alicia is an actress, although slightly more successful than Penny, having landed a role on CSI as a (dead) prostitute. Eventually, to Howard's delight, she and Penny get into a catfight over her treatment of the guys. After the altercation, Penny says Alicia is a "dead whore on TV; live one in real life" just before the gang hears Alicia having loud intercourse with a CSI producer.
- Bethany (Molly Morgan), Sarah (Sarah Buehler), and Skeeter (Andy Mackenzie): Characters who appear in "The Gothowitz Deviation" episode. Bethany and Sarah are a couple of women that Wolowitz and Raj meet in a Goth club. They then go to a tattoo parlor, where Skeeter is the tattoo artist. The name "Skeeter" is not used on the show, but appears in the credits.
- Christy (Brooke D'Orsay): An acquaintance of Penny's from Nebraska who had slept with enough of her relatives to make her "family", Christy suddenly moves in with Penny when she comes to California. Christy ends up having sex with Howard, forcing Penny to sleep on Leonard's couch. Howard then invites Christy to move in with him (and his mother). Mrs. Wolowitz and Christy end up having a fight, and the latter leaves. She also presents the guys other problems by reducing their foursome to three when playing Halo and dividing up their Chinese food order.
- Cole (Ryan Cartwright): An English student who works with Penny in the history class in Pasadena City College, introduced in the "The 43 Peculiarity" (season 6, episode 8). His appearance in Penny's life leads to Leonard's anxiety about his relationship with Penny.
- Dr. David Underhill (Michael Trucco): A MacArthur Genius Grant recipient, David is an experimental physicist like Leonard, who is excited to be working with him. With his leather jacket and handsome looks, Penny is shocked to know that David is a scientist and starts dating him. They break up when she finds out he is married.
- Dennis Kim (Austin Lee): Dennis is a 15-year-old child prodigy from North Korea who Dr. Gablehauser hopes to recruit into their Ph.D. program. Dennis and Sheldon have an antagonistic relationship when the former excels Sheldon in every way. The guys make arrangements so Dennis can meet girls of his age and get distracted from his own research. The plan succeeds and Dennis is seen kissing with a girl in the park, no longer an intellectual threat to Sheldon.
- Dmitri (Adam Gregor) He is the janitor of third floor in Caltech. But before he was a janitor, he was a physicist in Leningrad Polytechnical. After the collapse of the Soviet Union, he lost his job and had to move to the US. He seems to know a lot about physics. A question in the Physics Bowl about quantum electrodynamics stumped everyone but him.
- Dr. Elizabeth Plimpton (Judy Greer): A renowned cosmological physicist from Princeton University known for her work in quantum cosmology who comes as a personal guest of Sheldon in "The Plimpton Stimulation" episode and exhibits a strong sexual libido. Failing in her attempts to flirt with Sheldon, she engages in sexual intercourse with Leonard and Raj, and expresses a desire for a foursome with Leonard, Raj, and Wolowitz.
- Emily (Katie Leclerc): (Season 5) A deaf woman who Penny sets up with Raj. Since she is deaf, Raj finds that he can communicate with her despite his selective mutism. She shows interest in Raj when he spends a lot of money on her. Then Raj's parents get the bill, and force him to break up with her. Although Raj resists, he does tell Emily that all the gifts he gave her have to go back. She then loses interest in Raj.
- Gretchen (Briana Cuoco): Penny's former friend who stole her boyfriend and is at the same restaurant as Leonard and Penny which thoroughly annoys Penny especially after her ex- proposes to Gretchen. Gretchen is played by Kaley Cuoco's sister.
- Jesse (Josh Peck): A comic book store owner who is supposedly a rival of Stuart's comic book store. Stuart and Bernadette visit his store searching for a rare comic book, belonging to Howard, which Bernadette wants replaced after she accidentally brands it with her curling iron. Even though he appears smart and charismatic, he behaves as a jerk who belittles and humiliates Stuart in front of Bernadette inside his store; From Season 7, Episode 13 "The Occupation Recalibration".
- Jimmy Speckerman (Lance Barber): a former high-school jock who used to bully Leonard on a regular basis. He later contacts Leonard in "The Speckerman Recurrence", with an idea of inventing glasses that turn all movies into 3D. He is oblivious to the bullying nature of his actions against Leonard, having believed that they were "having fun" and describing him and Leonard as having been "a comedy team".
- Joy (Charlotte Newhouse): An exercise-freak woman who Leonard meets on a blind date set up by Bernadette via the "Girlfriend Pact" with Howard. Although Leonard finds Joy's mannerisms to be repulsive, he agrees to go out with her again based on hints she gives that she is easy.
- Lakshmi Choudry (Chriselle Almeida): a woman with whom Raj's parents set him up when he asks for a date to take to his cousin's wedding. He develops strong feelings for her and is willing to marry her, and she him. She tells him she is lesbian and is willing to marry him because she thinks he is gay and the ruse will fool her parents.
- Lalita Gupta (Sarayu Rao): A childhood acquaintance of Raj who bullied him, she is now a dental student at USC. Raj's parents set up a date for their son with her. During the date, Raj can only speak to her after drinking an alcoholic beverage (a "grasshopper") and acts very obnoxious, such as commenting on her childhood weight problem. Sheldon insists she bears a remarkable resemblance to Princess Panchali, an Indian princess in a children's story. Lalita is flattered at Sheldon's comments and attention. Eventually, Lalita leaves the obnoxious and drunk Raj to have dinner with Sheldon. Sheldon does not see her again because he "already has a dentist".
- Mrs. Latham (Jessica Walter): A wealthy widowed benefactor who takes a shine to Leonard at a donor/faculty get-together. She asks him out with the implication that he have sex with her in order to get the lab equipment his department needs. He at first resists, but after she says that she is going to fund his project anyway, he relents. Everyone at the University congratulates him for selling himself out for the money.
- Missy Cooper (Courtney Henggeler): Missy is Sheldon's twin sister who is intellectually and socially very much unlike him. Confident, tall and attractive, she immediately catches the attention of Leonard, Howard, and Raj. Sheldon realizes that within Missy's eggs lies the potential for another "superior mutation" like him. He temporarily elects himself as a guardian to Missy in order to choose the best mate for her (she rejects Leonard and Howard in favor of Raj, but his mutism derails any chance he might have with her). Missy objects to Sheldon deciding who she can sleep with, refers to Sheldon as "Shelly", and despite their differences she loves him and is proud of his accomplishments. Sheldon first mentions an unnamed sister in the first episode and again in the 7th season as an unseen character, where she gives birth to a son, and it is also mentioned that she is married.
- Prof. Rothman (Lynn Phillip Seibel): Professor Robb Rothman is a character that appears in "The Rothman Disintegration". He is an old theoretical physicist that worked at Caltech (Sheldon and Leonard's university) who was forced to retire because of inappropriate behavior (appearing nude in public, urinating in the university's particle physics lab etc.) and the belief that he was senile. After he leaves, Sheldon and Kripke fight over the possession of his office. He is also mentioned in "The Beta Test Initiation".
- Ramona Nowitzki (Riki Lindhome) and Kathy O'Brian (Emily Happe): A couple of graduate students, who both have a crush on Sheldon, and become his 'groupies.' Sheldon exploits them to get free food and perform personal services. Ramona first meets Sheldon after he introduced his work to graduate students. She claims to find Sheldon's work very stimulating and him very cute (much to the confusion of his friends). She arranges to have dinner with him in his apartment. The next few days she becomes a permanent presence in his life, pressuring him to concentrate on his research and avoid distractions such as video games, science-fiction television shows and weekend paintball expeditions. Sheldon gets tired of her, but is unable to dissolve their "relationship". Eventually, Sheldon reaches a breakthrough in his work to which Sheldon acknowledges that he could not have completed without her personal and mathematical assistance. Sheldon kicks Ramona out when she asks to share credit for the discovery. Afterwards, Kathy meets Sheldon in much the same way that Ramona.
- Siri (Becky O'Donohue): embodies Siri (software), the voice-recognition system used on certain smartphones and on which Raj developed a crush, because of its seductive voice. To which Howard jokingly states that "there is finally a woman in your life you can talk to". Raj has a dream about meeting her, represented by a beautiful woman, but he cannot speak to her in person due to his selective mutism, which causes him to awake from the dream screaming "NOOOOO!".
- Special Agent Angela Paige (Eliza Dushku): an FBI agent investigating Howard Wolowitz's background for a security clearance in "The Apology Insufficiency" episode. While interviewing the guys, Raj vomits on her shoes, Leonard hits on her, and Sheldon reveals too much information about Howard, and to add insult to injury, reveals too much information about Leonard.
- Spock (Leonard Nimoy): Sheldon's action figure Spock, the voice of Leonard Nimoy, appears to him in a dream convincing him to open his mint in-box 1975 Star Trek Transporter toy. After Sheldon breaks his toy and steals Leonard's, Spock reappears to Sheldon and convinces him to give Leonard his toy back.
- Summer (Sierra Edwards): Howard's "date" for the reception for Dr. Gablehauser in Season 1, Episode 4, "The Luminous Fish Effect". She is quite a bit taller than Howard and makes it apparent that the "date" is strictly a business event by telling Howard that "touching is extra".
- Toby Loobenfeld (DJ Qualls): A research assistant with a double major in Physics and Theater, Toby was used by Sheldon to play his fictional first cousin "Leopold Houston" from Denton, Texas, a character Sheldon invents as part of an elaborate lie told to avoid going to see Penny sing. Cousin "Leo" is a recovering drug addict who ends up cuddling with Penny on the couch, much to the chagrin of Leonard. He was also willing to argue with Sheldon on the subjects regarding drug use, showing knowledge on the subject.
- Wyatt (Keith Carradine): Penny's father. He comes to visit and Penny feels compelled to involve Leonard in a ruse to make him think that they are still together. (Wyatt reveals that he favors the successful Leonard over Penny's other "loser" boyfriends.) When the plot is revealed, he gets mad at Penny and feigns anger at Leonard. But after Penny leaves the room, he encourages Leonard to keep trying to get Penny back (because he wants his grandchildren to "grow up in a house without wheels"). Strangely though in the first episode where Leonard's mother visits, Penny tearfully reveals her rough childhood, saying that Wyatt wanted a boy and would call her "slugger". She does an imitation of what she wished her mother would say to her father: "'Bob, get over it, she's a girl, move on', but she didn't not one word!"
Appearing in one scene only
- Angelo (Peter Onorati): A barber who substitutes for Sheldon's regular barber, Mr. D'Onofrio, when Mr. D'Onofrio falls into a coma.
- Chen (James Hong): The owner of a Chinese restaurant (Szechuan Palace) which is regularly frequented by Leonard, Sheldon, Howard, and Rajesh. He appears most significantly in Season 1 Episode 17, where Sheldon engages in an argument concerning his belief that he is being served Orange Chicken rather than Tangerine Chicken. This leads to the exchange of several nonsensical remarks made by Sheldon (due to his lack of ability to speak Mandarin).
- Dr. Crawley (Lewis Black): An entomologist at the University, Dr. Crawley is visited by Sheldon, Howard, and Raj in order to identify the species of a cricket they found. He is agitated at losing his position at the university, his laboratory, and, as a result of an extended research trip, his wife. After his wife left him, he was forced to move in with his daughter, who lives in Oxnard, California "in the onion fields" (as opposed to its more glamorous beach areas).
- Mrs. Fowler (Annie O'Donnell): Amy Farrah Fowler's mother. She appeared in a webcam conversation with Amy and Sheldon in which they lie to her about the nature of their relationship, telling her that they are in a romantic relationship that includes coitus.
- Joan (Amy Tolsky): The court clerk that comes out to say there is only enough time for three more weddings, meaning Howard and Bernadette would not be able to get married before Howard left for his launch to the ISS.
- Joey (Eric André): A "petty functionary" as described by Sheldon who is the usher for a movie theater allowing patrons in to see the Raiders of The Lost Ark Midnight Screening. After allowing Wil Wheaton and his entourage access to the front of the line without tickets, Joey ultimately closes the theater in front of the guys after the movie has sold out.
- Joyce Kim (Ally Maki): A character who appears in "The Staircase Implementation", Joyce Kim was previously mentioned as a former girlfriend of Leonard; their relationship only lasted a month, after which she defected back to North Korea. However, in "The Staircase Implementation", Leonard admits that she was not a girlfriend, but a North Korean spy who attempted to get secrets from him by seducing him.
- Kevin (Blake Berris): A man who Penny meets during her 'non-date' with Leonard. He is writing a screenplay about his roommate who threw him out of their apartment for the evening.
- Louis (Ajgie Kirkland) A former occupant of the apartment in which Penny lives. He is a cross-dresser who Leonard mistakenly runs into in "The Staircase Implementation" episode, and who refers to Sheldon as "the crazy guy across the hall". The name Louis is used by Sheldon, referring to him/her as Louis/Louise.
- Octavia (Octavia Spencer): a clerk working at the California Department of Motor Vehicles who hands Sheldon a drivers permit after he refuses to take the test, but instead points out inaccuracies in the test. The name of the character is not used on the show, only in the credits.
- Professor Glenn (Rick Fox): A former professor of Bernadette's, who she reveals to Howard that she dated for a year. At 6'7", dark and handsome, Glenn is physically the polar opposite of Howard, leading the insecure Howard to feel like he will never measure up (literally as much as metaphorically).
- Sandy (Yeardley Smith): A bureaucrat who interviewed Sheldon for a menial job in "The Einstein Approximation". episode. Smith had a recurring role on Dharma and Greg as Marlene (both characters have similarities) a show previously co-created by Chuck Lorre. The name "Sandy" was not used on the show, but appeared in the credits. Smith also voiced the character of Lisa Simpson on The Simpsons.
- Sebastian (Steven Yeun) Sheldon's former roommate who left Sheldon on bad terms. Sebastian makes a single appearance in "The Staircase Implementation", where he tells Leonard to "run fast, run far" from Sheldon. His name is not used in the episode, but is listed in the credits.
- Venkatesh Koothrappali (Frank Maharajh): Raj's cousin, a lawyer in India, who tries to negotiate a deal for Raj's part of the One Ring prop from Lord of the Rings. He, by his own admission, is a bad negotiator, and does not get Raj the two jet skis that he wanted.
Notable guest stars appearing as themselves
A number of Hollywood celebrities and famous scientists have made appearances as themselves. The list is sorted by alphabetic order by last name.
- LeVar Burton (Season 4, "The Toast Derivation" and Season 6, "The Habitation Configuration"): Sheldon invited Burton to a party via a tweet. Upon opening the door and seeing the other guests at the party, Zack, Kripke, and Stuart (who at that moment was wearing nothing but a towel) singing karaoke, Burton leaves and when starting to walk down the apartment block stairs utters that he is "so done with Twitter". He appears again at the end of "The Habitation Configuration", taping an episode of "Fun With Flags" with Sheldon and Amy. Amy says "cut", followed by complaining that "this guy is worse than Wil Wheaton" (referring to Wil's appearance earlier in the episode). Sheldon then tells Burton that because Amy is his girlfriend, he is obligated to agree with her. Burton asks "I still get lunch, right?", to which Sheldon nods. Along with Brent Spiner and Wil Wheaton, Burton makes Star Trek: The Next Generation the most represented franchise on the show in terms of guest appearances.
- Ira Flatow (Season 3, "The Vengeance Formulation" and Season 7, "The Discovery Dissipation): In Flatow's Season 3 appearance (which was voice only) Sheldon is invited to talk about magnetic monopoles on Flatow's radio show, Science Friday. However, Barry Kripke pulls a prank on Sheldon by filling the room with Helium, and Sheldon is publicly humiliated to a nationwide audience when he spoke in a very high pitched voice. In Flatow's Season 7 appearance, Sheldon attends Ira Flatow's Science Friday radio program in person to be interviewed about Sheldon's recent semi-accidental discovery of synthesizing a new stable heavy element. While Ira is attempting to praise the nature and significance of the seemingly monumental discovery, Sheldon considers the accidental nature of it to be an extreme embarrassment and storms out of the radio studio leaving Ira speechless. On a later return visit to the Science Friday program with the invited Leonard and the uninvited Sheldon, Ira attempts to interview Leonard about his research which disproved Sheldon's discovery, but is interrupted by Sheldon who commandeers the interview and devolves it into an autobiography and yodeling demonstration. This causes Amy & Penny, who are listening to the program at home, to start a drinking game based on the embarrassing comments made by their respective boyfriends.
- Summer Glau (Season 2, "The Terminator Decoupling"): When the guys travel by train to a conference in San Francisco, they realize Summer Glau (who was in two science fiction television shows, Firefly and Terminator: The Sarah Connor Chronicles) is sitting in the same passenger car. Raj, Howard, and Leonard take turns talking with her. Raj cannot talk without drinking beer (which turned out to be non-alcoholic), Howard is his usual creepy, over-the-top self, and Leonard cannot start a conversation before she has to get off the train.
- Stephen Hawking (Season 5, "The Hawking Excitation", Season 6, "The Extract Obliteration" and Season 7, "The Relationship Diremption"): After Sheldon's much-anticipated meeting with Hawking, he discusses Sheldon's research and points out a mistake. Sheldon protests by saying that he does not make mistakes, to which Hawking replies "Are you saying that I do?" When Sheldon realizes his research does in fact contain a math error, he faints in embarrassment, prompting Hawking to remark "Oh, great, another fainter." Hawking later talks to Sheldon on the phone in "The Extract Obliteration", after beating him in a game of Words with Friends.
- James Earl Jones (Season 7, "The Convention Conundrum"): After Sheldon tries to form his own Comic-Con, he approaches Jones in a restaurant. After realizing Sheldon is a fan of Star Wars (in which Jones famously voiced Darth Vader), Jones invites him to have dinner with him, much to Sheldon's pleasure, and then Jones suggests spending the whole night together. The two later eat ice cream, go on a Ferris wheel, do Karaoke, pull a childish prank on Carrie Fisher, go to a strip club and a sauna, before Sheldon becomes disturbed by Jones and tells him his plan. Jones then offers to take Sheldon and his friends to Comic-Con with him, Sheldon's pleasure. The final scene ends with Jones reminiscing about a prank he did with old celebrities, and ends with Sheldon asking Jones who one of the celebrities was. In addition to Vader, Jones's role as Mufasa from The Lion King is also mentioned.
- Mike Massimino (Season 5, "The Friendship Contraction", "The Countdown Reflection", Season 6, "The Decoupling Fluctuation and "The Re-Entry Minimization", Season 8 "The First Pitch Insufficiency"): An astronaut who is a colleague of Howard during Howard's tenure at NASA's astronaut corps. Massimino reveals that his nickname is "Mass". Howard assumes the nickname is derived from Newton's second law, which states that force = mass times acceleration, but Massimino reveals that "Mass" is simply short for Massimino. Raj and Howard concoct an elaborate scheme to plant a seed in Massimino's mind to give Howard the nickname "Rocket Man" by having Howard set up the song "Rocket Man" as his ringtone on his cell phone, and Raj calling the cell phone during Howard's Skype conversation with Massimino. Their plan is thwarted when Howard's mother shouts to him that he needs to finish his Froot Loops, which triggers Massimino (and Dimitri) to give Howard the nickname "Froot Loops". He is heard on the phone in "The Launch Acceleration" and seen in the Soyuz capsule with Howard and cosmonaut Dimitri Rezinov, serving as their mission commander in "The Countdown Reflection".
- Katee Sackhoff (Season 3, "The Vengeance Formulation" and Season 4, "The Hot Troll Deviation"): Howard fantasizes about taking a bath with Katee Sackhoff (Captain Kara "Starbuck" Thrace in Battlestar Galactica). However, in his own fantasy Sackhoff scolds him and tells him to get a real girlfriend instead of imaginary ones. Sackhoff reappeared in a different fantasy of Howard's in "The Hot Troll Deviation", where she and George Takei help Howard realize that he still has feelings for Bernadette.
- George Takei (Season 4, "The Hot Troll Deviation"): During one of Howard's fantasies, Takei, along with Katee Sackhoff, help Howard realize that he still has feelings for Bernadette. Takei's real-life homosexuality is twice referenced in the episodes: once, when he first appears in Howard's fantasy, Sackhoff asks Howard if Takei's presence implies that Howard has homosexual tendencies, and the second reference occurs when Takei advises Howard about women's love preferences. Sackhoff asks Takei "How would you know?" and he responds "I read."
- Neil deGrasse Tyson (Season 4, "The Apology Insufficiency") Appears as a colleague of Raj. Upon being introduced to Tyson, Sheldon tells him that he (Sheldon) is upset at Tyson's role in the demotion of Pluto from planet status. Initially, Tyson explains that he had no role in the demotion, but later attempts to apologize to Sheldon. Sheldon declines the apology, immediately after he himself apologized to Howard, who declined Sheldon's apology.
- Wil Wheaton first appeared in the season 3 episode "The Creepy Candy Coating Corollary". See his entry in the recurring character section for more information.
- Buzz Aldrin (Season 6, "The Holographic Excitation"): Raj sends Howard a link showing a video that features Buzz Aldrin handing out candy to kids on Halloween. Aldrin gives space related candy, such as Milky Way and Mars bars, as well as Moon pies. He brags to the kids about his achievement of walking on the Moon, then taunts them with the line, "what have you done with your life?"
- Carrie Fisher (Season 7): While Sheldon is with James Earl Jones, the two go to Fisher's house in secret, where Jones warns Sheldon that Fisher has gone crazy in her old age. Jones then knocks on her door and runs off with Sheldon before Fisher exits her house and shouts, "It's not funny anymore, James!" While Jones replies, "Then why am I laughing?"
- Brian Greene (Season 4, "The Herb Garden Germination"): Sheldon and Amy attend a book signing of Greene's popular science book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos. At the event, Sheldon initially ridicules Greene in private conversations with Amy, but then he gets up and publicly ridicules Greene, asking Greene why does not he do something more useful with his time than write popular science, only to later state he was kidding.
- Stan Lee (Season 3, "The Excelsior Acquisition"): When Sheldon has to miss Lee's appearance at the comic book store because he ends up in traffic court after running a red light, Penny tries to make it up to him by taking him to Lee's house, uninvited and unannounced, having acquired Lee's address from Stuart. Lee, not impressed by the unexpected intrusion, sarcastically remarks "why don't you just come in and watch the Lakers game with me?" only for Sheldon, not understanding sarcasm, to rush into the house. Lee, annoyed, decides to apply for a restraining order. When Sheldon announces his "autographed" restraining order to Leonard, Howard, and Raj, he comments it will look great hanging next to his restraining order from Leonard Nimoy.
- Howie Mandel (Season 6, "The Re- Entry Minimization"): When Howard returns to earth he hears shouts of "Howie" and believes that the paparazzi is here for him until he learns that they were there for Mandel who had arrived at the airport at the same time as Howard. Mandel thinks Howard is delusional, proclaiming to his driver that during the entire flight, "he kept telling me he's an astronaut."
- Bill Nye (Season 7, "The Proton Displacement"): After Sheldon's childhood hero Professor Proton (Bob Newhart) contacts Leonard for assistance on an experiment, a jealous Sheldon befriends Nye, "The Science Guy".
- Charlie Sheen (Season 2, "The Griffin Equivalency"): When Raj discovers a celestial body he is very excited about it. At Penny's restaurant, Raj says to the patron at the next table over, "Hey, buddy. I'm going to be in People magazine!". Sheen turns around, takes off his sunglasses and says "Yeah? Call me when you're on the cover." (At the time, Sheen was starring in Two and a Half Men, also produced by Chuck Lorre.)
- George Smoot (Season 2, "The Terminator Decoupling"): After a train ride to a conference in San Francisco, Sheldon presents his paper to 2006 Nobel Prize laureate George Smoot, and proposes joint research. Smoot abruptly rejects his idea by asking "With all due respect, Dr. Cooper, are you on crack?"
- Brent Spiner (Season 5, "The Russian Rocket Reaction"): Sheldon shows up at a party thrown by his "mortal enemy", Wil Wheaton, only after he hears that Spiner will be there. After Wheaton gives Sheldon a signed, in-the-box Wesley Crusher action figure, Spiner grabs it and opens it, thus putting him on Sheldon's Mortal Enemies List immediately after Wheaton was removed from the list. Along with LeVar Burton and Wil Wheaton, Spiner makes Star Trek: The Next Generation the most represented franchise on the show in terms of guest appearances.
- Analeigh Tipton and Samantha Potter (Season 2, "The Panty Piñata Polarization"): Howard and Raj visit the America's Next Top Model house pretending to be cable television repairmen. Tipton and Potter made appearances, opening the door for Howard and Raj. Tipton greeted Howard and Raj, caught them in a lie as the house did not have cable television, but rather satellite, but allows them in regardless when Howard "corrects" his error with another lie when he says that they are satellite television repairmen. Potter did not get a speaking role (but was credited).
- Steve Wozniak (Season 4, "The Cruciferous Vegetable Amplification") Dines in Penny's restaurant at the same time that the guys are there. He compliments Sheldon for his "virtual presence device" (using Sheldon's name for the device without having heard how Sheldon calls it) and in turn Sheldon (having previously referred to him as "the Great and Powerful Woz") compliments Wozniak telling him that he ranks 15th on his list of favorite technological visionaries. When Wozniak feigns disappointment, Sheldon tries to console him by stating that the ranking is six places ahead of Apple founder Steve Jobs. Sheldon then tells Wozniak that the Apple II was rather "nifty" and is one of his proudest possessions. Wozniak promises Sheldon that he would autograph the computer if Sheldon brought it to him. In the haste to get the Apple II to Wozniak for signing, Sheldon trips and falls down the stairs, breaking the computer. Wozniak's wife also appeared in the scene, dining with Wozniak, but she was not credited.
- Masters, Megan (October 12, 2010). "Kaley Cuoco Returns to Big Bang Theory After Injury as a-Pregnant Amputee Bartender?!". Retrieved September 14, 2013.
- "The Middle Earth Paradigm". The Big Bang Theory. Season 1. Episode 6. October 29, 2007. 5:18 minutes in.
- "The Euclid Alternative". The Big Bang Theory. Season 2. Episode 5. October 20, 2008. CBS.
- "The Vegas Renormalization". The Big Bang Theory. Season 2. Episode 21. April 27, 2009. 9:42 minutes in.
- "The Luminous Fish Effect". The Big Bang Theory. Season 1. Episode 4. October 15, 2007.
- "The Guitarist Amplification". The Big Bang Theory. Season 3. Episode 7. November 9, 2009. CBS.
- "The Electric Can Opener Fluctuation". The Big Bang Theory. Season 3. Episode 1. September 21, 2009. CBS.
- "The Boyfriend Complexity". The Big Bang Theory. Season 4. Episode 9. November 18, 2010. 3:30 minutes in.
- "The Apology Insufficiency". The Big Bang Theory. Season 4. Episode 7. November 4, 2010. 12:50 minutes in.
- "The Countdown Reflection". The Big Bang Theory. Season 5. Episode 24. May 10, 2012.
- "The Psychic Vortex". The Big Bang Theory. Season 3. Episode 12. January 11, 2010. 8:25 minutes in.
- "The Grasshopper Experiment". The Big Bang Theory. Season 1. Episode 8. November 12, 2007.
- "The Cruciferous Vegetable Amplification". The Big Bang Theory. Season 4. Episode 2. September 30, 2010.
- "The Middle Earth Paradigm". The Big Bang Theory. Season 1. Episode 6. October 29, 2007.
- Ausiello, Michael (2009-01-23). "'Big Bang Theory' scoop: Sara Gilbert taken off contract". Ausiellofiles.ew.com. Retrieved 2010-10-04.
- Season 3 Episode 23 The Lunar Excitation
- "The Roommate Transmogrification". The Big Bang Theory. Season 4. Episode 24. May 19, 2011.
- "The Herb Garden Germination". The Big Bang Theory. Season 4. Episode 20. April 7, 2011. 19:08 minutes in.
- "The Stag Convergence". The Big Bang Theory. Season 5. Episode 22. April 26, 2012. 07:41 minutes in. CBS.
- "The Fish Guts Displacement". The Big Bang Theory. Season 6. Episode 10. December 6, 2012. Event occurs at 18:43. CBS. "Mike:So why'd you agree to come? Howard: Because Bernadette made me. Mike: I tried to back out too. My wife said I had to go. Howard: Your wife makes you do stuff? You're a big, scary cop! Mike: You're an astronaut and your wife makes you do things. And she's only 4 feet tall."
- "The Table Polarization". The Big Bang Theory. Season 7. Episode 16. February 27, 2014. Event occurs at 14:33. CBS. "Raj: ...know that we all love you and cherish you. Mike: Well, I wouldn't— Bernadette: (In warning tone) Daddy! Mike: You're great!"
- "The Thanksgiving Decoupling". The Big Bang Theory. Season 7. Episode 9. November 21, 2013. Event occurs at 3:54. CBS.
- "The Cooper/Kripke Inversion". The Big Bang Theory. Season 6. Episode 14. February 1, 2010. Event occurs at 17:53. CBS. "And can you please make that out to Bernadette? I was taken off the joint account until I learn the value of money."
- "The Einstein Approximation". The Big Bang Theory. Season 3. Episode 14. February 1, 2010. Event occurs at 06:29. CBS. "I know how to deal with stubborn children. My mother used to run an illegal daycare center in our basement."
- "The Creepy Candy Coating Corollary". The Big Bang Theory. Season 3. Episode 5. October 19, 2009.
- "The Vengeance Formulation". The Big Bang Theory. Season 3. Episode 9. November 23, 2009.
- "The Vengeance Formula". The Big Bang Theory. Season 3. Episode 9. November 23, 2009.
- "The Herb Garden Germination". The Big Bang Theory. Season 4. Episode 20. April 7, 2011.
- "The Roommate Transmogrification". The Big Bang Theory. Season 4. Episode 24. May 19, 2011.
- "The Stag Convergence". The Big Bang Theory. Season 5. Episode 22. April 26, 2012.
- "The Countdown Reflection". The Big Bang Theory. Season 5. Episode 24. May 10, 2012.
- "The Holographic Excitation". The Big Bang Theory. Season 6. Episode 5. October 25, 2012.
- "The Habitation Configuration". The Big Bang Theory. Season 6. Episode 7. November 8, 2012.
- "The Zazzy Substitution". The Big Bang Theory. Season 4. Episode 3. October 7, 2010. 5:53 minutes in.
- "The Flaming Spittoon Acquisition". The Big Bang Theory. Season 5. Episode 10. November 17, 2011. Event occurs at 11:44. CBS. Sheldon is seen looking at Stuart's Facebook page, where his name is seen to be "Stuart Bloom"
- "Big Bang Theory Makes 'Stuart' a Series Regular". TVLine.com. Retrieved August 22, 2012.
- "The Hofstadter Isotope". The Big Bang Theory. Season 2. Episode 20. April 13, 2009.
- "The Classified Materials Turbulence". The Big Bang Theory. Season 2. Episode 22. May 4, 2009.
- Sleasman, MaryAnn. The Big Bang Theory S6E13 blog at TV.com
- Sleasman, MaryAnn. The Big Bang Theory S6E13 blog at Tv.com
- "The Killer Robot Instability". The Big Bang Theory. Season 2. Episode 12. January 12, 2009.
- "The Friendship Algorithm". The Big Bang Theory. Season 2. Episode 13. January 19, 2009.
- "The Toast Derivation". The Big Bang Theory. Season 4. Episode 17. February 24, 2011.
- "The Maternal Capacitance". The Big Bang Theory. Season 2. Episode 15. February 9, 2009.
- "The Jerusalem Duality". The Big Bang Theory. Season 1. Episode 12. April 14, 2008.
- "The Bat Jar Conjecture". The Big Bang Theory. Season 1. Episode 13. April 21, 2008.
- "The Cornhusker Vortex". The Big Bang Theory. Season 3. Episode 6. November 2, 2009.
- "The Griffin Equivalency". The Big Bang Theory. Season 2. Episode 4. October 13, 2008.
- "The Mommy Observation". The Big Bang Theory. Season 7. Episode 18. March 13, 2014.
- "The Panty Piñata Polarization". The Big Bang Theory. Season 2. Episode 7. November 10, 2008.
- "The Irish Pub Formulation". The Big Bang Theory. Season 4. Episode 6. October 28, 2010. CBS.
- "The Infestation Hypothesis". The Big Bang Theory. Season 5. Episode 2. September 22, 2011. CBS.
- "The Good Guy Fluctuation". The Big Bang Theory. Season 5. Episode 7. October 27, 2011. CBS.
- "The Lizard-Spock Expansion". The Big Bang Theory. Season 2. Episode 8. November 17, 2008.
- "The White Asparagus Triangulation". The Big Bang Theory. Season 2. Episode 9. November 24, 2008.
- "The Vartabedian Conundrum". The Big Bang Theory. Season 2. Episode 10. December 8, 2008.
- "Big Bang Theory: We didn't anticipate how protective the audience would feel about our guys". Variety. May 5, 2009. Retrieved March 7, 2010.
- "The Status Quo Combustion". The Big Bang Theory. Season 7. Episode 24. May 15, 2014. 20:01 minutes in. CBS.
- "The Lunar Excitation". The Big Bang Theory. Season 3. Episode 23. May 24, 2010.
- "Pilot". The Big Bang Theory. Season 1. Episode 1. September 24, 2007.
- "The Financial Permeability". The Big Bang Theory. Season 2. Episode 14. February 2, 2009.
- "The Dead Hooker Juxtaposition". The Big Bang Theory. Season 2. Episode 19. March 30, 2009.
- "The Dumpling Paradox". The Big Bang Theory. Season 1. Episode 7. November 5, 2007.
- "The Bath Item Gift Hypothesis". The Big Bang Theory. Season 2. Episode 11. December 15, 2008.
- "The Pork Chop Indeterminacy". The Big Bang Theory. Season 1. Episode 15. May 5, 2008.
- "The Cooper Extraction". The Big Bang Theory. Season 7. Episode 11. Dec 12, 2013.
- "The Cooper-Nowitzki Theorem". The Big Bang Theory. Season 2. Episode 6. November 3, 2008.
- "The Loobenfeld Decay". The Big Bang Theory. Season 1. Episode 10. March 24, 2008.
- "The Jiminy Conjecture". The Big Bang Theory. Season 3. Episode 2. September 28, 2009.
- "The Einstein Approximation". The Big Bang Theory. Season 3. Episode 14. February 1, 2010.
- Goldberg, Lesley (2 October 2013). "'Big Bang Theory' Books Bob Newhart's Return, Adds Bill Nye". The Hollywood Reporter. Retrieved 28 October 2013.
- "(#402) "The Cruciferous Vegetable Amplification"". the Futon Critic. Retrieved September 9, 2010.