Leonard Hofstadter - wikipedia Leonard Hofstadter Not to be confused with Lennard Hofstede. hide This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article describes a work or element of fiction in a primarily in - universe style. Please help rewrite it to explain the fiction more clearly and provide non-fictional perspective. ( January 2010 ) This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. ( December 2010 ) Leonard Hofstadter Johnny Galecki as Dr. Leonard Leakey Hofstadter The Big Bang Theory character Portrayed by Johnny Galecki First appearance `` Pilot '' ( 2007 ) Created by Chuck Lorre Bill Prady Profile Occupation Experimental physicist show Family Family Beverly Hofstadter ( mother ) Alfred Hofstadter ( father ) Michael Hofstadter ( brother ) Unnamed sister Floyd ( uncle ) Nancy ( aunt ) Spouse Penny Other relatives Wyatt ( father - in - law ) Susan ( mother - in - law ) Randall ( brother - in - law ) Leonard Leakey Hofstadter, Ph. D., is a fictional character in the CBS television series The Big Bang Theory, in which he is portrayed by actor Johnny Galecki. Leonard is an experimental physicist, who shares an apartment with colleague and best friend Dr. Sheldon Cooper ( Jim Parsons ). For his portrayal, Galecki was nominated for a Primetime Emmy Award and a Golden Globe Award in 2011. It is possible that Leonard is based on the show 's co-creator, Bill Prady, back when he was a computer programmer. Leonard has been described as the straight man of the series. Penny ( Kaley Cuoco ) is Leonard 's next - door neighbor and main love interest, and the teasing of romance between the two of them is a major force driving the series. In `` The Gorilla Dissolution '', they finally become engaged, marrying in Las Vegas at the beginning of season 9. Contents 1 Creation and casting 2 Personality 3 Family 4 Work 5 Relationships 6 See also 7 References Creation and casting Leonard is named after actor / producer Sheldon Leonard, and Nobel Prize in Physics Laureate Robert Hofstadter. Johnny Galecki was originally asked to play the role of Sheldon Cooper, but thought he would be `` better suited '' for the character of Leonard. Leonard is one of four characters to appear in every episode of the series, along with Sheldon, Howard Wolowitz and Raj Koothrappali. Personality Originally from New Jersey and a graduate of Princeton University, Leonard works as a Caltech experimental physicist, mainly working with lasers, and shares an apartment with colleague Sheldon Cooper in Pasadena, California. He is usually seen wearing his characteristic black thick - framed glasses, low - cut black Converse All Stars sneakers, pastel hoodies or neutral - colored sweat jackets ( i.e. jackets with integrated hoodies ) or a combination of the two, brown or red trousers ( or, less frequently, jeans ), and physics - themed T - shirts. His various girlfriends have tried to change his outfits : Penny had no success while Stephanie got him to wear dress shirts and sweaters ( which he found uncomfortable ), and Priya got him to briefly switch to dress shirts, waistcoats and dark slacks ; he reverted to his original outfits after she left for India, but started eschewing his hoodies in favor of button - down shirts and non-hooded jackets towards the end of the seventh season, a trend that continued into successive seasons. Although Leonard feels at home with his geek colleagues, he wants to be more social. Among the main characters, he is the one who has almost no difficulty interacting with `` non-geek '' individuals. He is instantly captivated by Penny, and from the beginning sets out to date her. In early episodes, Leonard is reluctant to let Penny know about his recreational activities ( such as Klingon Boggle ), as he does not want her to see him as a geek. While certainly a geek by most definitions, he is far less socially inept than Sheldon ( who is unable to grasp social norms and is often even dismissive of them ), Raj ( who was unable to talk to women unless he was under the influence of alcohol or anti-anxiety prescription drugs, and even after getting over his handicap still tended to speak inappropriately ), and Howard ( who was often seen as `` creepy '' when flirting with women, including Penny ). Leonard is also musically inclined, as he can play the cello, although he holds the bow upside down and plays on the finger board. As seen in the season 1 episode `` The Hamburger Postulate '', he and Leslie Winkle practice their instruments and then leave to have intercourse, which Leonard calls `` a little musical foreplay ''. Despite his attempts to not appear to be a geek, Leonard owns, among other things, Star Wars hygiene products, a prop of the One Ring, Star Trek and Star Trek : The Next Generation officer 's uniforms, an expansive Superman comic book collection ( and wears Clark Kent - type glasses ) and a Battlestar Galactica Colonial warrior 's flight suit. Early in the series, Leonard tried to get rid of his collectables to impress Penny with his maturity. However, he changed his mind when he saw that Penny was already dating another man. Because he has lived with Sheldon for several years, Leonard knows him better than his other colleagues : this has led Sheldon to believe ( slightly erroneously ) that Leonard is his best friend. Nevertheless, Leonard often finds himself explaining Sheldon 's behavior or serving as a mediator between him and other people in many situations. For instance, when Penny and Sheldon engaged in a fierce dispute, Leonard gave Penny Sheldon 's mother 's phone number so she would call her son and scold him for his behavior, thus ending the fight. `` The Staircase Implementation '' features a flashback to when Leonard first moved in with Sheldon. Leonard explains to Penny that he moved in despite the difficulty of living with Sheldon because the rent was so reasonable. Shortly after moving in, during a rocketry experiment Leonard, Raj and Howard conducted, Sheldon observed miscalculations Leonard made in mixing the rocket fuel and managed to avert disaster by grabbing the fuel and placing it in their apartment building 's elevator. The resulting explosion disabled the elevator, thus explaining why the elevator is out of order for the duration of the series. Leonard explains that Sheldon, despite his tendency to alienate others, kept quiet about Leonard 's destruction of the elevator. ( Leonard cites : `` He did n't rat me out to the landlord, or the police... or Homeland Security. '' ) Despite Leonard 's reasonable and friendly personality, he occasionally demonstrates a mean streak. These include deliberately triggering Sheldon 's obsessive compulsive problems, mocking Howard and Raj whenever they slip up, and making sniping comments when Penny 's commitment issues flare up. He is also prone to jealousy, often feeling insecure and defensive whenever Penny interacts with another guy, and on one occasion trying to frighten off a British college student she was doing a project with, because Penny commented positively on his accent. Leonard 's primary health concern is his lactose intolerance : his consuming melon or any dairy products ( and according to the pilot episode, even corn ) results in flatulence. Leonard wears eyeglasses because of myopia, and can not see without them. On one occasion, when his glasses were broken at the movie theater, he had to surreptitiously return to his apartment and retrieve his backup glasses. In order to avoid detection by a sick Sheldon and Penny, who was nursing him, Howard and Raj helped him to navigate through the living room by using a helmet camera. Leonard also states in one episode that he suffers from sleep apnea. During his relationship with Leslie Winkle, he tells her that many members of his family have died from heart disease and thus he has a genetic disposition to the condition. Family All of the members of Leonard 's family are accomplished scientists, except for his younger brother Michael, who is a tenured law professor at Harvard University. Leonard 's mother, Dr. Beverly Hofstadter, is a psychiatrist and neuroscientist. She has a personality almost identical to Sheldon 's, including strict speech patterns, lack of social conventions, and attention to detail, and she is principally responsible for Leonard 's difficult childhood. Sheldon and Beverly have a friendly relationship where they share details of each other 's lives, with Sheldon often failing to pass on significant information to Leonard such as Leonard 's parents divorcing and the family dog Mitsy 's death. Leonard is upset with the fact that she tells Sheldon more than she tells him, but later decides it 's okay. After a night out of bonding and drinking with Penny in which she notices an attractive busboy, Beverly kisses Sheldon but realizes she `` would rather have the busboy ''. Due to his mother 's views, Leonard never celebrated his birthday or Christmas when he was a child, and when she visited him she was not impressed with his unoriginal research. Leonard revealed to Penny that he built a `` hugging machine '' when he was young in order to compensate for the lack of affection from his mother. He further stated that his father used to borrow it. Beverly also belittles Leonard by pointing out that his brother and sister are more successful in their respective fields than he is. Leonard 's brother, Michael, is a Harvard law professor and is engaged to the youngest appellate court judge in New Jersey history ( and has since gone on to work with a Habitat for Humanity-esque organisation ), and his older sister, whose name is unknown, is a cutting - edge medical researcher working with gibbons to cure diabetes. However, Beverly admits in season 11 that Leonard married the best out of his siblings, after she develops a genuine friendship with Penny. Leonard also dislikes his memories of Christmas, not just because he never celebrated it, but also because instead of gifts the Hofstadter kids had to turn in papers to `` Santa '' which were graded the next day. Over the course of six years he never got over a `` C minus '', which according to Sheldon was a true gift, because by Sheldon 's lights he never deserved anything better. It is implied that at the end of the episode `` The Peanut Reaction '', Leonard begins to celebrate his birthday after Penny decided to throw him one after hearing that he had never had one ; And one implication is at the end of the episode `` The Russian Rocket Reaction '' when Leonard asked Brent Spiner to come to his birthday party. As for Christmas, Leonard has learned and come to love it as an adult, unlike Sheldon. Leonard had two childhood pets, a cat named Dr. Boots Hofstadter and a dog named Mitsy. Leonard 's father, Dr. Alfred Hofstadter is an anthropologist. Sheldon reveals that Leonard 's middle name, `` Leakey '', comes from famed anthropologist Louis Leakey, with whom Leonard 's father had worked. Leonard is embarrassed by his middle name and its humorous connotations, and rarely mentions it, as the name is an obvious embarrassment. Apparently his father was not very affectionate towards him either ; he mentions that he had to compete with the bones of an Etruscan boy for his father 's attention, but this was likely because his father was away from home a lot for work and was n't able to get to know his children well. However, they seem to have developed a good, affectionate rapport by the time of Leonard and Penny 's impending second wedding ceremony in the season 9 finale. Though little is known about Leonard 's extended family, a few references to it have been made. In the first episode, Sheldon and Leonard discuss Leonard 's grandmother, who had visited them on Thanksgiving the year before. She has Alzheimer 's disease and apparently `` had an episode '' during her visit, which resulted in her stripping off her clothes and carving the turkey. On Beverly 's first visit, she tells Leonard that his uncle Floyd has died, which greatly upsets him ( according to him, Floyd was the only family member he really liked and of whom Leonard has warm memories from his childhood ). Leonard also has several other uncles, whom Sheldon says are all very bald ; when they gather together, they look `` like a half carton of eggs. '' Leonard describes his aunt, however, as `` one of the hairiest women you 'll ever meet ''. He also mentioned an Aunt Nancy, apparently a `` crazy cat lady '' who had 25 cats, died, and was eaten by them. Work Leonard has an IQ of 173, and was 24 years old when he received his PhD from Princeton University. Leonard also received a dissertation of the year award for his doctoral paper on experimental particle physics. Leonard has been established to have been a child prodigy, and a gifted scientist with an impressive knowledge of theoretical physics. His work as an experimental physicist often includes the use of lasers, such as a helium -- neon laser or free - electron laser, and his research topics have varied from Bose -- Einstein condensates and foundations of quantum mechanics to soft cosmic rays at sea level and development of novel rocket propellants. Leonard designs experiments in order to test theories but, according to Sheldon, his work is mostly derivative and thus unimportant. Although Leonard 's attempts to disprove the existence of dark matter were made moot by the work of another physicist, Leonard helped to solidify proof of the hypothetical matter 's existence with a photomultiplier, and was invited as keynote speaker to a topical conference by the Institute of Experimental Physics for his successful research on super solids. From the season 6 finale, `` The Bon Voyage Reaction '' Leonard heads to the United Kingdom to work on a physics project seeking the hydrodynamics equivalent of the Unruh effect, sponsored by Professor Stephen Hawking, for three months on a ship in the North Sea. Relationships Kaley Cuoco ( who portrays Penny ) and Johnny Galecki at PaleyFest 2013 Leonard became interested in Penny almost immediately after seeing her for the first time. His infatuation with Penny becomes the major force that drives the series during the first few seasons. By the end of the first season, Leonard finally manages to ask Penny out, and they have their first date. Subsequently, they break up because Penny felt she was not as smart as Leonard would like. Besides Penny, Leonard has been involved with only a few other women. One of Leonard 's former girlfriends who is mentioned on several occasions is Joyce Kim, who did not appear until the third season. Leonard 's friends recalled on many occasions that they were together for only 27 days, after which Joyce, later revealed to be a spy, defected to North Korea. Initially, after feeling that Penny was not for him, Leonard turned his attention to fellow scientist Leslie Winkle. The first time Leonard asks Leslie out, she rejects him, and his further relationships with her proved to be only short - lived casual sexual encounters that only happened to satisfy Leslie 's libido. Leslie briefly started dating Leonard in Season 2, but when he failed to back her up in an argument with Sheldon, she dumped him. In the second season, Leonard began a stable relationship with a physician named Stephanie Barnett. Although the relationship went well, even earning Sheldon 's approval, Leonard felt uncomfortable with Stephanie moving in with him, and the relationship ended. On another occasion, when Leonard 's mother was visiting, he and Penny came very close to having sex, but Leonard ruined the moment by suggesting that they were burying their lifelong issues with their parents by doing so, which offended Penny. In the second - season finale, when Leonard, Sheldon, Howard, and Raj were due to leave for a three - month scientific expedition to the North Pole, Penny privately expresses sadness, and wishes that he would not leave. In the third season premiere, Leonard and Penny finally started a romantic relationship and had intercourse for the first time. However, the relationship ended after eight months, after Leonard told Penny he loved her and took umbrage at her inability to reciprocate, which led to friction that was exploited by guest star Wil Wheaton who appeared as a fictionalized version of himself, who observed and exacerbated it in order to break them up in the middle of a bowling match Wheaton 's team was having against Leonard, Penny, Sheldon, Howard and Raj. Shortly after his breakup with Penny, in `` The Plimpton Stimulation '', Leonard has a one - night stand with Dr. Elizabeth Plimpton ( Judy Greer ), a physicist he admires, when Sheldon invited her to stay in their apartment for a brief visit. This encounter causes some tension between Leonard and Penny, who is somewhat judgmental of Leonard 's doing so. However, the two later resolve their feelings and their friendship continues. In the third - season finale, `` The Lunar Excitation '', after Penny 's failed attempts to move on from her relationship with Leonard, she becomes intoxicated and has sex with him. In the morning, Leonard believes that their relationship has resumed, though Penny tells him that the previous night was a mistake. This causes a strain on their friendship ; at the end of the episode, Leonard becomes intoxicated and tries to have intercourse with her, prompting Penny to push him out of her apartment, to which Leonard suspects a double standard. He immediately makes the same advances towards Leslie Winkle, who replies, ' Let me think about it '' and slams the door in his face. Throughout the fourth season, it becomes obvious that Penny is still in love with Leonard. It is unclear whether or not Leonard has noticed this, though he clearly is still interested in Penny. In `` The Benefactor Factor '', an older rich woman propositions Leonard in exchange for a large donation to the physics department ; he initially resists and she admits that she planned to make the donation anyway, after which they engage in a one - night stand. Leonard arrives home the next morning, whereupon Penny recognizes his `` walk of shame '' and Sheldon thinks Leonard has a future in becoming a gigolo to rich ladies in exchange for donations. Leonard also has an affair with Raj 's younger sister Priya ( apparently every time she comes to town ), despite a pinky swear with Howard that neither of them would attempt to make a move on her, and Raj giving his strong disapproval. When Priya returns, she and Leonard begin a relationship. Raj strongly opposes this, and Penny is secretly uncomfortable with Leonard dating someone else, eventually breaking down and crying while talking with her friend Amy Farrah Fowler. Once again, Leonard is unaware of Penny 's true feelings. Subsequently, Priya pressures Leonard into ending his friendship with Penny, which he attempts with extreme reluctance. Penny complies, though it is clear that she does not want Leonard out of her life. Penny eventually resolves to stay in Leonard 's life by ingratiating herself to Priya. In the Season 4 finale, Leonard runs into Penny and Raj as they come out of his room in the morning, just after Leonard and Priya appear to break up upon Leonard 's learning that Priya is soon moving back to India. At the start of Season 5, Leonard and Priya are trying to maintain a long - distance relationship via Skype ( including a failed attempt at cybersex ) with Priya continuing to treat Leonard like a submissive partner. Despite being the most eager to have sex, Leonard proves he is quite awkward in these situations. Leonard later goes to a wedding with Amy, and they seem to take a liking to each other, though Sheldon disapproves, karate - chopping Leonard and saying, `` She 's not for you... not for you ! ''. Later, despite feeling that he and Priya were in love and might get married, Leonard finds himself attracted to a comic book artist named Alice. The attraction is mutual, and they even share a kiss. Right when they are about to have sex, however, he tells Alice that he has a girlfriend, thus ending the relationship. Leonard then decides to confess his behavior to Priya via Skype, but he is shocked to learn that Priya has also betrayed him, sleeping with her former boyfriend ; Priya defends that they both slipped up a little, but Leonard corrects her saying that he slipped a little, while she slipped a lot, bringing the conversation to a strained end. In the next episode, Leonard tells Sheldon that he is single, implying that he and Priya have broken up ; his actions since then have confirmed their split occurred. Through the fourth and fifth seasons, Penny was still single and dating, though when intoxicated, she has confessed that she regrets breaking up with Leonard. In `` The Ornithophobia Diffusion '', Leonard and Penny go to the movies as friends. Leonard decides that since they are no longer dating, he can be honest and does not have to pay for everything or do whatever Penny wants. The two bicker all evening and sabotage each other 's attempts to chat up people in the bar. Penny admits that she likes the new, more assertive Leonard. Leonard sees this as another opportunity to grovel and try to get Penny to sleep with him, so she leaves. On the spur of the moment in `` The Recombination Hypothesis '', Leonard asks Penny out on a date after he imagines what getting back with her might be like. Their real date ends successfully and they agree to take their relationship slow in `` The Beta Test Initiation. '' During their renewed relationship Penny has dismissed comments about him ever leaving or dumping her or about worrying about his unfaithfulness around other women and strippers as in the episode `` The Stag Convergence ''. After Penny suggested having sex in `` The Launch Acceleration '', Leonard breaks the mood by proposing to her accidentally. They later meet and Penny does have the courage to tell him `` no '' and not break up with him as she did two years previously when he told her that he loved her. However, their relationship is still obviously strained. In season 5, Leonard and Penny watch Howard being launched into space while holding hands to comfort each other. With the start of season 6, he wants a reluctant Penny to define their relationship in `` The Date Night Variable ''. Penny finally does admit her love to Leonard, in `` The 43 Peculiarity ''. Penny and Leonard awkwardly stare at each other before running off in opposite directions. Leonard, though, is buoyed by optimism over Penny 's admission. Alex Jensen asks Leonard out to dinner in `` The Egg Salad Equivalency '', which boosts Leonard 's ego because two beautiful women are interested in him, however, Alex 's interest makes Penny insecure. After another dispute with Sheldon, Leonard tries to move in with Penny in `` The Spoiler Alert Segmentation '', however she is not ready. During their Valentine 's Day dinner in `` The Tangible Affection Proof '', Leonard again tries to propose to Penny and she cuts him off quickly. She admits that she is very happy with him, but she also admits to commitment issues and the thought of being married forever really `` freaks '' her out. Leonard then tells her that when she is ready to get married, she can propose to him. In the season finale, Leonard leaves for an overseas job for four months and Penny is confident enough in their relationship to wait for him. In `` The Gorilla Dissolution '', Leonard and Penny become engaged. Throughout season 8, a running gag is their reluctance to decide upon a wedding date. In the season 8 finale, Penny asks Leonard to marry her that night in Las Vegas. Leonard happily accepts, but during the journey, after Penny expresses happiness that they will get married while knowing everything about each other, Leonard confesses to having shared a drunken kiss with another woman while on the boat in Europe, though he adds that the woman started it and he rejected her. Penny becomes hurt by the revelation, and even though she claims to forgive Leonard, there is clearly tension between them, leaving the season ending in a cliffhanger as to whether or not they will go through with the wedding. At the beginning of season 9, Leonard and Penny marry, although not without some initial problems. They both reveal that they were subconsciously trying to sabotage their relationship, feeling unworthy of the other. Leonard, concerned that he was trying to sabotage his relationship with Penny, meets with the woman he kissed on the boat. She barely remembers the incident and quickly grows bored with Leonard 's ramblings, taking a sarcastic and dismissive tone toward him. From that meeting Leonard comes to terms with his insecurities and he and Penny are able to become more comfortable in dealing with their mutual fears about their relationship. Leonard seriously tries to move into Penny 's apartment though Sheldon has serious objections and makes them compromise to spend multiple nights a week in Leonard 's old room. Early in season 10, the couple is very happy to be finally living alone after Sheldon moves in with Amy. See also List of The Big Bang Theory characters References Jump up ^ `` The Middle - Earth Paradigm ''. The Big Bang Theory. Season 1. Episode 6. October 29, 2007. 05 : 16 minutes in. CBS. Jump up ^ `` The Big Bang Theory : The Complete First Season ''. Bullz-eye.com. Retrieved January 15, 2010. Jump up ^ `` Oak Park native finally gets the girl in ' Big Bang ' ''. Chicago Tribune. January 10, 2010. Archived from the original on January 14, 2010. Retrieved January 15, 2010. ^ Jump up to : `` The Gorilla Dissolution ''. The Big Bang Theory. Season 7. Episode 23. May 8, 2014. Jump up ^ `` ' Big Bang Theory ' : ' We did n't anticipate how protective the audience would feel about our guys ' ''. Variety. May 5, 2009. Retrieved February 5, 2010. Q. Are Sheldon and Leonard named after the brilliant ( producer ) Sheldon Leonard of `` The Andy Griffith Show '', `` The Danny Thomas Show '', `` The Dick Van Dyke Show '', `` My Favorite Martian '' and `` I Spy ? '' ( Binnie ) A. Yep. Chuck and I are both fans. Chuck 's idea. Jump up ^ The Big Bang Theory, la fórmula perfecta del humor ^ Jump up to : `` Pilot ''. The Big Bang Theory. Season 1. Episode 1. September 24, 2007. Jump up ^ `` The Nerdvana Annihilation ''. The Big Bang Theory. Season 1. Episode 14. April 28, 2008. Jump up ^ `` The Panty Piñata Polarization ''. The Big Bang Theory. Season 2. Episode 7. November 10, 2008. ^ Jump up to : `` The Pancake Batter Anomaly ''. The Big Bang Theory. Season 1. Episode 11. March 31, 2008. Jump up ^ `` The Peanut Reaction ''. The Big Bang Theory. Season 1. Episode 16. May 12, 2008. ^ Jump up to : `` The Maternal Capacitance ''. The Big Bang Theory. Season 2. Episode 15. February 9, 2009. Jump up ^ `` The Middle Earth Paradigm ''. The Big Bang Theory. Season 1. Episode 6. October 29, 2007. 05 : 20 minutes in. Jump up ^ `` The Codpiece Topology ''. The Big Bang Theory. Season 2. Episode 2. September 29, 2008. 11 : 14 minutes in. CBS. Jump up ^ `` The Codpiece Topology ''. The Big Bang Theory. Season 2. Episode 2. September 29, 2008. 11 : 40 minutes in. CBS. Jump up ^ Season 4 Episode 3, `` The Zazzy Substitution. '' First aired October 7, 2010. Jump up ^ `` The Bat Jar Conjecture ''. The Big Bang Theory. Season 1. Episode 13. April 21, 2008. ^ Jump up to : `` The Benefactor Factor ''. The Big Bang Theory. Season 4. Episode 15. February 10, 2011. ^ Jump up to : `` The Bad Fish Paradigm ''. The Big Bang Theory. Season 2. Episode 1. September 22, 2008. Jump up ^ `` The Cooper - Hofstadter Polarization ''. The Big Bang Theory. Season 1. Episode 9. March 17, 2008. Jump up ^ `` The Tangerine Factor ''. The Big Bang Theory. Season 1. Episode 17. May 19, 2008. Jump up ^ `` The White Asparagus Triangulation ''. The Big Bang Theory. Season 2. Episode 9. November 24, 2008. Jump up ^ `` The Fuzzy Boots Corollary ''. The Big Bang Theory. Season 1. Episode 3. October 8, 2007. Jump up ^ `` The Hamburger Postulate ''. The Big Bang Theory. Season 1. Episode 5. October 22, 2007. Jump up ^ `` The Codpiece Topology ''. The Big Bang Theory. Season 2. Episode 2. September 29, 2008. Jump up ^ `` The Lizard - Spock Expansion ''. The Big Bang Theory. Season 2. Episode 8. November 17, 2008. Jump up ^ `` The Vartabedian Conundrum ''. The Big Bang Theory. Season 2. Episode 10. December 8, 2008. Jump up ^ `` The Monopolar Expedition ''. The Big Bang Theory. Season 2. Episode 23. September 21, 2009. Jump up ^ `` The Electric Can Opener Fluctuation ''. The Big Bang Theory. Season 3. Episode 1. September 21, 2009. Jump up ^ Sheldon indicated that Leonard and Penny 's initial Season 3 relationship lasted eight months in the first Act of `` The Zazzy Substitution '' ( Episode 4.3 ). Jump up ^ `` The Lunar Excitation ''. The Big Bang Theory. Season 3. Episode 23. May 24, 2010. Jump up ^ `` The Irish Pub Formulation ''. The Big Bang Theory. Season 4. Episode 6. November 4, 2010. Jump up ^ `` The Prestidigitation Approximation ''. The Big Bang Theory. Season 4. Episode 18. March 10, 2011. CBS. Jump up ^ `` The Engagement Reaction ''. The Big Bang Theory. Season 4. Episode 23. May 12, 2011. CBS. Jump up ^ `` The Pulled Groin Extrapolation ''. The Big Bang Theory. Season 5. Episode 3. September 29, 2011. 18 : 05 minutes in. CBS. The Big Bang Theory Characters Leonard Hofstadter Sheldon Cooper Penny Howard Wolowitz Raj Koothrappali Episodes Season 1 `` Pilot '' Season 2 `` The Terminator Decoupling '' Season 3 `` The Jiminy Conjecture '' Season 4 `` The Cruciferous Vegetable Amplification '' `` The Hot Troll Deviation '' `` The Love Car Displacement '' `` The Toast Derivation '' `` The Roommate Transmogrification '' Season 5 `` The Skank Reflex Analysis '' `` The Infestation Hypothesis '' `` The Wiggly Finger Catalyst '' `` The Russian Rocket Reaction '' `` The Rhinitis Revelation '' `` The Good Guy Fluctuation '' `` The Isolation Permutation '' `` The Flaming Spittoon Acquisition '' `` The Shiny Trinket Maneuver '' `` The Recombination Hypothesis '' `` The Beta Test Initiation '' `` The Werewolf Transformation '' `` The Hawking Excitation '' `` The Stag Convergence '' `` The Countdown Reflection '' Season 6 `` The Fish Guts Displacement '' `` The Santa Simulation '' `` The Egg Salad Equivalency '' Season 7 `` The Hofstadter Insufficiency '' `` The Convention Conundrum '' Season 8 `` The Locomotion Interruption '' Season 9 Season 10 Season 11 Recurring concepts `` Soft Kitty '' Related articles Awards and nominations Bazinga ( jellyfish ) Euglossa bazinga Young Sheldon Portal Book Retrieved from `` https://en.wikipedia.org/w/index.php?title=Leonard_Hofstadter&oldid=855362960 '' Categories : Fictional characters from Pasadena, California Fictional characters from New Jersey The Big Bang Theory characters Fictional physicists Fictional characters introduced in 2007 Male characters in television Fictional victims of bullies Hidden categories : Use mdy dates from March 2015 Articles that need to differentiate between fact and fiction from January 2010 All articles that need to differentiate between fact and fiction Articles that may contain original research from December 2010 All articles that may contain original research Articles with multiple maintenance issues Talk Contents About Wikipedia Català Čeština Español فارسی Français Italiano עברית Latina Magyar Македонски Nederlands Norsk Português Română Русский Slovenčina Svenska Türkçe Українська 中文 12 more Edit links This page was last edited on 17 August 2018, at 19 : 02 ( UTC ). 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Question: why did penny and leonard break up in season 3
Answer: Leonard told Penny he loved her and took umbrage at her inability to reciprocate, which led to friction that was exploited by guest star Wil Wheaton who appeared as a fictionalized version of himself, who observed and exacerbated it in order to break them up in the middle of a bowling match Wheaton's team was having against Leonard, Penny, Sheldon, Howard and Raj