Leonard Hofstadter

Leonard Hofstadter is the deuteragonist of The Big Bang Theory. Leonard is the leader of Team Leonard. Just like Sheldon Cooper, he also wants to win a Nobel prize.  Leonard is friends with Howard Wolowitz, Rajesh Koothrappali, Amy Farrah Fowler, Bernadette Rostenkowski-Wolowitz, Stuart Bloom, and sometimes Sheldon Cooper who was his roommate. He has a girlfriend named Penny. They had an on and off relationship. But it is back on and they are married. Sheldon can be antagonizing on the show and the reason why Leonard puts up with him because he saved his life in the elevator and owes him his life when they first met. 
Many times Leonard wanted to move out of the apartment and want to ditch Sheldon. But mostly he puts up with him because he is like a tag-along little brother. 
He was portrayed by Johnny Galecki. He was also portrayed by Isaac Harger as a child. 
==Early Life (Before the series)==
Leonard was born on May 17, 1980, in New Jersey to Alfred and Beverly Hofstadter (Same month that Mt. St. Helens' erupted and "The Empire Strikes Back" came out.). Not much is known about his early life. He has two siblings: a younger brother named Michael and an elder sister.
 
He did not celebrate his birthday or Christmas as a child due to his mother having the family study the holidays for their "anthropological and sociological implications on society" and only celebrating achievements in the family.
The family wrote research papers for Christmas and they were returned graded with his stocking. As Leonard was a geek, he was bullied badly as a youth and he stopped growing in the eighth grade. 
Before he went to Princeton, his parents put him in advanced placement classes, and sent him to learn the cello, Leonard had his first kiss at age 19 to a girl named Geraldine Coco.
After graduating from high school, Leonard attended Princeton University and got his doctorate at age 24. In 2003, he met Sheldon Cooper, with whom he began sharing an apartment, but not before meeting Howard Wolowitz and Rajesh Koothrappali. The 4 guys became a group and hung out often. On June 30, 2004, Leonard and Howard made a Girlfriend Pact. The pact was that when one of the two got a girlfriend, they would have that girlfriend set the single guy up with a female friend of her own.
==Character Journey==
=== Season 1 ===
Leonard, Sheldon, Howard and Raj meet Penny and Leonard instantly falls in love with her ("Pilot" (S1E1)).
===Season 2===
His first date with Penny went well, but they broke up shortly afterwards because Penny thinks that he'll only date a girl with a college degree. He goes on to date Stephanie and Leslie, but both of those relationships don't last very long (Stephanie and Leonard broke up after only three episodes, while Leslie dumps him and then starts a friends-with-benefits relationship with Howard). Leonard finds out near the end of the season that Penny has feelings for him. Just before he leaves for his trip to the North Pole, she gives him a thick blanket, along with a hug. After he leaves, she tells herself, "I wish you weren't going."
===Season 3===
Leonard and Penny start dating, though at first, they have some trouble trying to be more than friends, they eventually start a stable and loving relationship.
In "The Creepy Candy Coating Corollary", while in bed, Leonard tells Penny about his Girlfriend Pact with Howard meaning that if one of them got a girlfriend, she would set the single one up with one of her friends. Later, Howard meets Bernadette who is not able to find anything in common with Howard until they both find out they have overbearing mothers.
While in bed one night after sex, Leonard admits to Penny for the first time that he loves her. Penny is troubled by the potential serious turn in the relationship because she has commitment issues and can not respond in kind, and she breaks up with Leonard. They do work things out to remain friends.
===Season 4===
Leonard begins a relationship with Raj's sister, Priya Koothrappali. Penny is devastated. She admits that Leonard is a great guy and she should have never broken up with him.
===Season 5===
Leonard ends his relationship with Priya after learning that she slept with her ex-boyfriend. In the 100th episode, he reconnects with Penny and they resume their relationship, establishing a "beta-test" to ensure that they don't face the same problems as the last time they were together. At the end of the season, Leonard asks Penny to marry him for the first time.
===Season 6===
Penny almost breaks up with Leonard because, to her, the relationship seemed boring; however, she visits him at work and is re-impressed with how smart he is and their relationship seems to take off from there. They become more committed to and dependent upon each other during the rest of this season. Penny eventually admits to Leonard that she loves him, and soon faces serious issues when Sheldon's new assistant gains a crush on Leonard, but the issues diminish when Leonard assures Penny that he's not turning his back on her. Leonard leaves for a North Sea expedition in the season finale, with the two of them now comfortable enough in their relationship to say they love each other.
===Season 7===
Upon his return from the trip, Leonard and Penny's relationship starts to get very serious. They do plenty of gestures for each other, and at the end of the season, they become engaged to be married.
===Season 8===
Leonard and Sheldon come up with a new scientific theory that gives them recognition, while at the same time, Penny and Leonard's relationship continues to improve, including a minor situation regarding finances and living arrangements that won't upset Sheldon. In the last episode of the season, thanks to some prodding by Sheldon to set a date for their wedding, Leonard and Penny take off to Las Vegas to get married.
===Season 9===
Leonard and Penny arrive at a Las Vegas wedding chapel. They later hear about the Shamy break up and get married with their friends watching over webcam, but only Howard and Stuart catch their "Husband and Wife" pronunciation part. They then have a terrible fight about Leonard's accidental indiscretion and return to their own apartments (The Matrimonial Momentum). Leonard meets up with Mandy to talk with her and later, he and Penny reconcile and Sheldon gives them a wedding gift: Tickets to San Francisco (The Separation Oscillation). In "The Positive Negative Reaction", they discuss having children one day. Because of the surprise elopement not sitting well with everyone, Penny and Leonard decide on having another ceremony to renew their vows, with their friends and family attending.
===Season 10===
Leonard and Penny have their re-wedding ceremony at a park which is officiated by Bernadette (The Conjugal Conjecture).
In "The Fetal Kick Catalyst", Penny is signing autographs for fans of the first and second Serial Ape-ist movies where the fans think that she is a terrible actress and can't believe that the nerd Leonard is her husband. The fans sit around Leonard as he tells his story how he won the hot actress, which makes them think of him as awesome.
Leonard and Penny finally have their own apartment: Apartment 4A, with Sheldon having moved out to live with Amy in Apartment 4B, first as a living experiment (The Cohabitation Experimentation), but then permanently (The Veracity Elasticity).
===Season 11===
In "The Proposal Proposal", Leonard is happy about Sheldon and Amy's engagement. Bernadette suggests that Leonard and Penny should have a baby in order to try and calm Howard and Bernadette's worries about having another baby so soon, but Leonard and Penny declined.
In "The Retraction Reaction", Leonard is interviewed by Ira Flatow on NPR but screws up in the interview. Later, it seemed that he was right about what he said.
In "The Matrimonial Metric", Sheldon picks Leonard to be his best man for his wedding. He and Penny are Shamy's wedding party.
===Season 12===
In "The Decision Reverberation", Leonard starts to be more confident in himself and talks President Siebert into making him a co-lead on a new experimental physics project.
In "The Maternal Conclusion", Leonard finally makes amends with his mother after all these years.
In the last episode, "The Stockholm Syndrome", Penny learns that she is pregnant. One smart and beautiful child in the oven.
==Relationship with Penny==
Leonard is instantly captivated by the presence of Penny during the "pilot episode", and from that moment he sets his mission to date her. By the end of the pilot episode, he has already announced to Sheldon "our babies will be smart and beautiful." Sheldon is quick to add, "not to mention imaginary" though, by series end, Penny is pregnant.
His infatuation with Penny becomes the major force that drives the series during the first season. They did go out to dinner one night with Penny thinking that the other guys were going to join them and Leonard making excuses for them. She asks later at her door if this night was a date; however, Leonard denies it though he doesn't mean it. At the season one finale, Leonard finally managed to ask Penny out, and they had their first date after Penny has a bad breakup.
 Subsequently, they broke up because Penny felt she wasn't as smart as Leonard would like and that she'd need a college degree to date Leonard. On another occasion, during the visit of Leonard's mother, Leonard and Penny came very close to having sex, but he ruined the moment by talking about their childhood issues with his mother and her father, respectively.
In the second season finale, when the guys were going on a 3-month scientific expedition, Penny finally showed interest in Leonard but kept her feelings a secret. Out of hearing range, Penny admits to herself that she wishes he was going to be gone all summer.
In the third season premiere, Leonard and Penny finally started a romantic relationship kissing him as soon as he returned and making love for the first time. They remain to have a stable relationship and even had the blessing from his mother during her second appearance during the episode, "The Maternal Congruence".
The relationship eventually came to an end during "The Wheaton Recurrence" after Penny was not able to tell Leonard that she loved him  (Although, Penny had been manipulated by Wil Wheaton to end the relationship and rush out, forcing Sheldon's team to forfeit a bowling match.) Leonard and Penny decided during "The Spaghetti Catalyst" that they should stay friends even though they broke up (for Sheldon's sake). Penny's father would later beg Leonard to "not give up on her".
In "The Isolation Permutation", Sheldon became angry when he had to spend the night consoling a heartbroken Amy from being left out of the bridesmaid dress shopping by Penny and Bernadette. He told Howard and Leonard to keep their women in line. Leonard responded that he should not be the person to do that since he was no longer Penny's boyfriend. Sheldon responded that since Leonard was the person who invited Penny to lunch ("Pilot") when she moved into the apartment, everything about her is on Leonard.
In "The Ornithophobia Diffusion", Leonard agreed to go out with Penny to a movie just as friends, their first attempt at going out alone together since they broke up. The first half of the non-date went well, with the two watching a movie that Leonard picked, a documentary about building a dam on a river in South America. Penny actually had to pay for her own ticket after Leonard pointed out that they were not on a date and sex was off the table. Later at Brady's Beer, they start to argue and interfere with the people they are trying to flirt with. Back at home, Leonard told that he did not think they were ready to go out as friends and apologized for his behavior. Penny apologized too but said that she liked the take-charge and cocky Leonard.
On the spur of the moment in "The Recombination Hypothesis", Leonard asks Penny out on a date after he imagined what getting back with her might be like. Their real date ends successfully and they agreed to take their relationship slow in "The Beta Test Initiation", by treating it as a Beta test and present Bug reports to each other to settle any issues arising.
In "The Friendship Contraction", things seem to move along well with their second attempt at a relationship. During a blackout at the apartment, Leonard decided to hang out at Penny's and they had wine, played with a bubble wrap, and attempted to make out before being interrupted by Sheldon.
In "The Werewolf Transformation", Penny learns the game of chess and beats Leonard the first time she plays. They later picked Sheldon up from Amy's apartment after he went there at 3 a.m. after playing with his bongos in Apartment 4A.
In "The Weekend Vortex", Leonard checks in with Penny whether she would be okay with him spending a whole weekend on a 48-hour Star Wars online gaming marathon. Penny does not seem disturbed by it, which upsets Leonard a little. He doesn't want her upset. Penny asks him what he expects her to say so Leonard tells her that he expects her to at least show that she is upset at the prospect of him being unavailable for the entire weekend. Acting she gets upset, then lets him do it realizing that he is a wild stallion that needs to run free.
In "The Launch Acceleration", Penny suggested that they move up their relationship and get intimate; however, Leonard ruins the mood when he asks her to marry him. 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.
In "The Countdown Reflection", there was some friction between the two of them about the proposal, but when Howard was being launched they were holding hands to comfort each other.
In "The Date Night Variable", Raj, who was butting into their date, insisted that Penny tell Leonard how she felt, but she was not ready and she threw him out of the apartment. Leonard wants to talk to Penny about their relationship, but Penny says that she has had a hard day and wants to just hang out.
Penny is expressing doubts about her feelings for Leonard, though she claims to be happy with the relationship in "The Decoupling Fluctuation". She almost tells Leonard about her doubts and then ends up sleeping with him after looking into his sad eyes. Sheldon's pretty new graduate assistant Alex Jensen flirts with Leonard in "The Higgs Boson Observation", which he doesn't realize, but Penny does take note. When Alex visits and mistake Penny for his lab assistant, Penny takes him back to her place and wants to pull his pants off with her teeth. She doesn't want Leonard to lose interest in her.
In "The Holographic Excitation", Penny revs up their relationship by becoming more acquainted with his work and seducing him in his lab more than once.
In "The 43 Peculiarity", Penny is working with a fellow English student named Cole, who's working with her on an oral class project. Leonard is jealous and follows him down the apartment stairs and tells him to watch out for "Penny's boyfriend" since he was a mean gang member. Penny is upset with Leonard and the two later meet in the hallway and have an argument. Penny tells him that she cannot believe that he cannot trust her and that he embarrassed her in front of Cole who knew who he was since his picture is on her refrigerator. Penny continues to tell him that he is the one she is with and accidentally mentions that he knows that she loves him. Leonard is stunned and tells her that that is the first she ever said that. Penny rushes off to work crying.
In "The Egg Salad Equivalency", after Alex asks Leonard out to dinner and didn't tell Penny about it, she begins to feel really insecure about their relationship. Leonard apologizes by showing up at her door playing a little ditty on his cello. She decided instead of feeling bad, she would do something about it. First, she looks into science classes at college, but they sound boring. Then she buys some geek glasses to look smart, which does have a positive effect on Leonard as he takes her into his bedroom.
In "The Tangible Affection Proof", Leonard takes Penny out to dinner for Valentine's Day. Penny feels that all the efforts never meet the expectations and she will end up disappointed. At dinner, Penny sees an old boyfriend proposing to the girl that broke them up. Leonard again tries to propose and Penny stops him. They begin to argue in front of Howard and Bernadette who have their own issues that night. Later after they barely say good night, Leonard tells Penny that she ruined the whole evening. Penny finally admits that she has commitment issues. She is so happy right now that she knows they are going to eventually get married and since it is forever, that scares her. Leonard then puts the responsibility of proposing on her and that she should do it when she's ready. In the end, she does ask him to be her valentine.
In "The Closure Alternative", Penny was concerned about the passion Leonard showed for science, comics and various television shows while she had no passion in her life. Her dreams had always been to become a famous movie star and live a glamorous life. Anything less than that she felt was settling. Her epiphany comes that she is passionate about her boyfriend Leonard and all her wonderful friends.
In "The Bon Voyage Reaction", Leonard takes a job working on a Stephen Hawking expedition in the North Sea for four months over the summer. Penny will miss him but knows that it is a good opportunity and sends him off. At the airport, she is fussing over him like a wife sending him off on a business trip. She also has to watch Sheldon over the summer, too.
In "The Hofstadter Insufficiency", Leonard hurts Penny because he seems to be having such a great time on the ship; she thinks that he is not even missing her. In "The Deception Verification", Leonard makes up for it by showing up early and hides in her apartment so that they can spend time together a couple before telling the gang that he's back. It works until Amy and Sheldon find them together after they think that Penny is cheating on Leonard.
In "The Romance Resonance", Howard makes a romantic gesture to Bernadette by writing her a song. Leonard mentions that Penny never does anything like that, except for sex which doesn't count. Penny is determined to romance Leonard. Raj can only suggest that she cook for him or reenact a scene from a romantic movie. Finally, after a candle lit dinner, Penny puts on some romantic music, spreads rose petals into her neatly cleaned bedroom and present Leonard with the first edition of his favorite book from when he was growing up, "The Hitchhiker Guide to the Galaxy". Unfortunately, Leonard had already purchased the book after they had seen it in a used bookstore together. Penny gets upset telling him about all the thoughtful things he had done for her and shows him her collection.
An aeroplane ticket, a rose given to her "just because" and the eleven-page letter he wrote her after the first time they slept together. Leonard was very touched that she kept all these things. He then kisses her, showing that Penny did do something romantic.
In "The Thanksgiving Decoupling", Penny reminisces about a Thanksgiving she had in Las Vegas with her ex-boyfriend, Zack Johnson which included one of those silly fake weddings. Penny appears devastated when her friends inform her that the wedding was real and she is Mrs. Zack Johnson. Penny and Leonard argue about how quickly she should get her annulment so Penny invites Zack over to their Thanksgiving dinner at Howard's mother. Zack appears as dimwitted as ever telling them that breaking up can be hard on the kids which they don't have. Finally, Penny and Leonard reconcile and she tells him that the next time she gets married it will be for real, for life and (jokingly) or for money and lovingly strokes his chin.
In "The Cooper Extraction", Amy points out to the gang that most of them would not know each other if Sheldon had not been part of their lives. Penny feels that Leonard would never have successfully asked her out at the Cheesecake Factory, while Leonard suggests that she would have ended up with Zack. In the Zack story, he spent all the rent money on some magic beans. Leonard might have moved in with Raj; however, he thinks that he would be eating Raj's cooking too much and would be overweight since he didn't have a girlfriend. 
In "The Hesitation Ramification" and "The Occupation Recalibration", Penny gets a part in the TV series "NCIS" and is very disappointed when her scene is cut and not aired. Frustrated and tipsy, she sees her life crumbling when Leonard reminds her that she still has him. She agrees with him and probably to show some advancement in her life, she kneels down and proposes to him. All Leonard can utter is "Umm", much like when he wouldn't succumb to her drunk advances after her Halloween party in "The Middle Earth Paradigm".
Penny gets very upset since she doesn't think he wants to marry her. After she storms out, Leonard is afraid to ask her if their relationship is now over.
The next day he does visit Penny who assures him that they are still together and that he did the right thing not agreeing to her proposal because she was a mess. Now she has rethought her career and decides to quit the Cheesecake Factory and focus all of her time on acting. Leonard does support her though he is obviously worried about her to give up her only source of income. The proposal count currently is two to one.
In "The Table Polarization", the gang wants to add a dining room table to Apartment 4A which Sheldon objects to. Penny gets Leonard to pick out a dining set that she likes and gets Leonard to stand up more against Sheldon. Sheldon objects to Penny changing Leonard to stand up against him. Penny points out that Amy has changed Sheldon who agrees and then decides to break up with Amy.
In "The Friendship Turbulence" Penny's car breaks down and she is afraid she has to go back to work at The Cheesecake Factory. Leonard later pick's up Penny so she can get her old job back. She is not thrilled to go back since she left telling the bitches goodbye and that she'll see them at the Oscars. Leonard tries to make Penny feel better by lightening the mood; however, he is treading a thin line between her loving him because he's trying, and her hating him for making her feel worse. He opens the door of a strange car that Penny mentions is not his. He pulls out a key and tells her that he thought they would take her car revealing he's brought a new one for her. The car is nothing fancy, but she can use it to go to auditions and doesn't have to return to her old job. Penny is both shocked and touched; she hugs and kisses Leonard tightly.
In "The Mommy Observation", Penny seems to feel that if she were a successful actress and had to move around, Leonard would leave his job even if it was a tenured position to follow her since she would be making more money. They get complimented when Stuart says that they are the best couple he knows.
In "The Proton Transmogrification" Penny asks Leonard to marry her to get their marriage proposal rejection score from 2 to 1 to even. She also gets upset when she keeps getting all the Star Wars in-jokes during their "Star Wars' Day" celebration.
In "The Gorilla Dissolution", Leonard and Penny get back in her apartment after getting fired from her movie. Penny wants to start making smarter decisions about her life. She says that they could get married and Leonard asks her to be serious. Leonard asks her if he is a smart decision, like choosing a healthy boring bran muffin. Penny doesn't care what pastry he is because she is CHOOSING HIM. Leonard is still talking about being a pastry like a strawberry Pop-Tart that she is excited about. Penny tells him to forget about it. Leonard does want to marry her but feels that she is just feeling sorry for herself because she was fired.
Penny explains that it may seem that way, but getting fired made her think that fame and fortune are not what is going make her happy. Leonard wants to know what she needs. "You, you stupid Pop-Tart!" Leonard finally says that he guesses that he is in, which also bothers Penny. Leonard then retorts that it is an excited "I guess I'm in!" and they agree that they are engaged which seems somewhat anti-climactic.
To change the mood, Leonard pulls a ring out of his wallet that he has had for a couple of years, gets down on one knee and asks Penny formally. Penny says "yes" and he slips the ring on her finger that still has ape hair glued to it and they embrace.
In "The Status Quo Combustion", Leonard and Penny announce their engagement; however, the gang is more excited about Raj and Emily hooking up. Leonard goes searching for the missing Sheldon and finds him at the railroad station leaving town to think about all the changes in his life. Leonard wants him to come home, but Penny convinces him that he should let him go.
In "The First Pitch Insufficiency", they go on a double-date with Shamy where Sheldon is bragging about their relationship is so much better than theirs. Shamy has an 8.2 out of ten for relationship stability based upon well-proven criteria. Leonard looks at it; however, Penny doesn't want to take the test. She already has his doubts and doesn't need them confirmed. They are engaged and still have very little in common which scares her. It also scares Leonard, but he still wants to face all their problems together. His reassurance really touches Penny and Amy who would like Sheldon to say things like that.
In "The Prom Equivalency", Amy and Bernadette throw a do-over prom on the roof of the apartment building. Penny is at first reluctant to attend the party because they always disappoint her, but Leonard tells her that he really wants to take the most beautiful girl to the prom, this time. She wears her old red prom dress. The roof is decorated wonderfully and Penny really gets into the mood. While others are still getting there, Penny and Leonard dance along without any music on the roof. First, they conclude that they probably would not have approached each other if they had been at the same prom. They are both definitely in a romantic mood, while Penny is also glad they aren't having the drama normally seen at proms.
In "The Space Probe Disintegration", Leonard tells Sheldon that his attitude is why he and Penny are not living together. After a tearful period thinking about them him moving out, Sheldon lets him go one night a week to stay at Penny's. Sheldon still sleeps on her couch that night.
In "The Commitment Determination", Sheldon keeps pushing them for a wedding date. The couple insists that they aren't in a hurry, are in a good place emotionally and are concentrating on their careers. Thinking about the wedding details they decide on a small church wedding dressed in black tie tuxes and no releasing of butterflies. Suddenly Penny smiles and sits closer to Leonard. She tells him that she's free that night. They could go to Vegas and just get married. Leonard agrees. Sheldon is happy for them, but still doesn't want them to sit in his spot. Driving to Vegas, Penny is very happy and glad that they took their time to get to know each other. No surprises and no regrets. Leonard has one regret, from where he was drunk and made out with a woman on his North Sea expedition. Penny was not happy but still wants to marry him.
In "The Matrimonial Momentum", Leonard and Penny are at a wedding chapel and decide on their wedding package, which includes a live stream that allows their friends to watch from home. In the chapel, the minister asks Leonard and Penny if they had prepared vows. Penny is surprised that Leonard has and he says that they are made from atoms that have travelled over 14 billion years to create them so they can come together as a couple and make each other whole, which overwhelms Penny. Penny sweetly says that he is the love of her life and her best friend and improvises, quoting the lyrics to 'You've Got a Friend in Me' from the Disney film "Toy Story". The minister asked if that was from "Toy Story," Penny says it was and Leonard loves it. Leonard gets misty-eyed and confirms that he does. Leonard and Penny are pronounced man and wife. Unfortunately, Stuart and Howard are the only ones remaining who catch it, due to Sheldon insulting Amy, causing her to finally break up with him, causing most of the group to leave. Leonard decides to carry Penny across the threshold into the suite, but huffs and puffs as he carries his wife into the hotel room.
They kiss, but Penny still can't stop thinking about Mandy, the girl on the boat. Leonard again insists that the kissing wasn't that great, especially since he also chipped her tooth. Penny wants to know if he feels guilty. Leonard jokingly says that he does not feel guilty because the girl had dental insurance. Leonard then adds that he does feel guilty when he sees her every day at work, freezing when he quickly realizes his mistake. Penny is now truly shocked that he never told her this fact. Instead of spending the night in Vegas, they return back to their apartments, still fighting. Leonard sadly spends his wedding night with Sheldon, who isn't surprised at all.
In "The Separation Oscillation", Leonard finally confronts Mandy, his kissing buddy from the North Sea, about the incident and it doesn't seem to mean much to her. Leonard also realizes that he really was trying to sabotage the relationship. He talks with Penny and tells her. She too realizes she has been trying to sabotage their relationship. Leonard then confesses, "I've loved you from the moment we met and I will keep loving you until the end of time." Penny is very touched and tells him that that was the most beautiful thing anyone has ever said to her. He follows with getting down on one knee and asks, "Penny Hofstadter, will you please stay married to me?" She accepts and they reconcile, kiss and head into the bedroom to formalize their marriage.
In "The 2003 Approximation", Leonard finally moves out of his apartment and eventually moves in with Penny into her apartment. The sleeping arrangements are still a little complicated. Even though they are living together in 4B, they sometimes sleep in 4A, in Leonard's old room. This is due to Penny having a change of heart at the last minute after feeling sorry for Sheldon who was having a hard time dealing with his breakup with Amy and Leonard moving out. In "The Helium Insufficiency" it is also apparent that Leonard is still maintaining an office in 4A.
In "The Valentino Submergence", Leonard and Penny go out to dinner for Valentine's Day but the wait is at least one hour and they suffer through an unsympathetic maître'd. Penny's decision to flirt with him gets nowhere and she gets called "ma'am". She tries to get him to acknowledge that they are almost the same age; however, he is 21 and she is 31. Next, she drags Leonard out of the restaurant because she is still young. After a fast food meal in the car, they look for something young and fun to do. The "Moulin Rouge" movie is too late, no skinny dipping or dancing either. They end up dressed as cupids breaking in on Sheldon's "Fun with Flags" programs yelling "Happy Valentine's Day" and that they are "young and fun".
In "The Positive Negative Reaction", Leonard and Penny talk about having children one day. Penny says she is not in a rush, but someday they can. Leonard adds that he thinks they would make amazing parents.
In "The Big Bear Precipitation", while spending the weekend in a cabin, Penny learns that Leonard has been keeping a secret bank account for emergencies because he doesn't feel that Penny can handle money due to her large credit card debt. Penny, who makes more than him, admits that she does not like her job having to flirt to get her sales; however, she will keep at it because it is the responsible thing to do.
In "The Viewing Party Combustion", Leonard gets tired of the quarterly Roommate Agreement meetings where nothing important is ever discussed. Penny who has signed the latest one as an occupant of the apartment and wants to attend since she gets to lead them in the pledge. Leonard sulks about attending the meeting which makes Penny mad driving her and Sheldon over to her apartment breaking the group into two separate camps. Leonard also points out the weird brother/sister relationship she and Sheldon have which Amy is also jealous of. Penny often takes Sheldon's side due to her sibling feelings for him.
In "The Convergence-Convergence" Leonard has invited his dad to his and Penny's wedding re-do and has to deal with his divorced parents. He just wants everyone to be civil. After delivering a toast to Penny thanking her for a wonderful year of marriage, his father exasperated with his ex-wife leaves with Mary Cooper. They find a connection in their mutual hatred of Beverly and appear to hook up much to Sheldon and Leonard's discomfort, meaning they could end up being step-brothers.
In "The Conjugal Conjecture"; the actual ceremony is officiated by Bernadette. Penny tells him how much she loves him and how glad they did elope. Leonard just tells her how much he loves her and that he can't believe she is with him.
In "The Cohabitation Experimentation", Sheldon and Amy move into Penny's apartment for a five-week cohabitation experiment after Amy's apartment suffers a plumbing problem. The Hofstadter's are so excited about finally having a place of their own that they put on music (which Sheldon would never let them do) and have a private dance party in their underwear.
In "The Fetal Kick Catalyst", Penny is signing autographs for fans of the Serial Ape-ist movies where the fans think that she is a terrible actress and can't believe that the nerd Leonard is her husband. The fans sit around Leonard as he tells his story how he won the hot actress.
In "The Veracity Elasticity", Leonard learns from Howard that Penny has secretly been moving his collectables into storage. Although he's mad that she doesn't feel guilty about it, he does understand that she really hasn't been feeling comfortable like she belongs there. He allows her to redecorate their room any way she wants it. Upon seeing Penny's new design for the bedroom, he immediately hides some of her stuff in her old closet.
In "The Birthday Synchronicity", Bernadette has a false alarm trip to the hospital before she has her baby interrupting both Lenny and Shamy who are trying to have sex.
In "The Holiday Summation", the Hofstadter's cheerily head off to cut their first live Christmas tree and have a horrible experience. Leonard lets go of the axe sending it flying, the tree slips of the car roof while driving it home, Leonard collapses under the tree while carrying it up The Stairs and after getting it into the apartment, they find an animal lurking in the tree. The tree ends up being shoved down The Elevator shaft.
In ”The Romance Recalibration”, Penny feels that Leonard is no longer trying in their marriage; specifically he sits around in his underwear playing video games and never brings her flowers. Leonard thinks that he is the only one in their marriage that has ever worked at it. Leonard follows Penny to the spa that she took Amy instead of him and they decide that they do have some challenges in their marriage. Reluctantly, both ask Sheldon to prepare them a Relationship Agreement like his and Amy especially since he and Amy appear to be so happy living together.
In "The Emotion Detection Automation", Leonard and Penny have an argument over her brother Randall coming to Pasadena and staying with them, an argument where Leonard's friendly, reasonable and thinking-carefully personality goes the other way around.
In "The Escape Hatch Identification", Beverly thinks Leonard and Penny are trying to keep their "terrible" marriage intact since they took Raj in for a while and also asked Randall to live with them, which is not true since Leonard and Penny are okay in their marriage and are not looking for roommates, but are instead being generous to let someone they know quite well to live with them until they can get a house of their own.
In "The Proposal Proposal", Bernadette suggests that Leonard and Penny should have a baby in order to try and calm Howard and Bernadette's worries about having another baby so soon, but Leonard and Penny say "no". They also celebrate their second wedding anniversary, which they'd forgotten about.
In "The Bitcoin Entanglement" (S11E09), Leonard and Penny visit Zack to reclaim Leonard's old laptop that Penny had given him years ago. Zack also shows them an old video a drunk Penny made after she broke up with Leonard seven years before. She did love him but was scared of a permanent commitment. 
In "The Conjugal Configuration", Larry Fowler is hiding out in Sheldon and Amy's apartment. Mrs. Fowler comes over demanding that her husband return. He decided to take a break from their marriage. His wife comes over to talk things over with Penny and decides that she is a good person and they should become friends. Penny marches over to 4B and demands that Larry goes home. Penny gets mad at Leonard when he compares their relationship to the bickering Fowlers, but she lightens up when he re-evaluates what he said.
In "The Procreation Calculation", Penny declares that she doesn't want to have children because their life is so great as it is. Leonard is disappointed and then declares that that is one thing on his bucket list that he'll never do like when he wanted to own a Batmobile. In the end, Penny does rent him a Batmobile for the day.
In "The Imitation Perturbation", Leonard reminds Penny of their first kiss on their couch during her Halloween party as they host one for the gang. Penny can't remember it until she admits that she does, but she was drunk and mad at Kurt. She would rather remember their first official kiss as at Leonard's birthday party where she gave it freely. Leonard agrees that that will be their first official kiss.
In "The Grant Allocation Derivation", he has to distribute some excess grant money which he takes very seriously. Penny finds that very sexy until Leonard can't decide between the last three.
In "The Propagation Proposition", Zack and his new wife Marissa want to have a baby, but Zack is infertile. They decide to ask Leonard to help them out since he thinks he's nice and smart. Leonard said yes and wanted to help them out. Penny was against it and then said that he could do it since she had decided to not have any children without considering what Leonard thought about it. Leonard at first was willing to help them out until he decided he didn't want a child in the world that he and Penny weren't going to raise ("The Donation Oscillation"). Also, Penny realizes with her father's help that she's doubting her "no child" decision, especially when she's under the impression that she's letting everybody down.
In "The Decision Reverberation", Penny again tells Leonard that he should stand up for himself more. Leonard decides that he wants to be the principal investigator on a plasma physics study so he prepares a proposal and plans to threaten to quit if President Siebert will not accept his proposal. Penny is worried about him quitting because she doesn't want to move. Even though President Siebert turned him down, Leonard does get called back and offered a different job as co-lead on a photo entanglement project. Leonard is happy and Penny is very proud of him.
In "The Change Constant", the Hofstadter's and the Cooper's are waiting for the Nobel Committee to call from Sweden. Kripke gives them a fake phone call calling them suckers. Amy then gets the call and quietly says that they won. Sheldon can't believe her so Leonard slaps him, then they all shout excitedly and have a big hug together. Leonard had had permission to slap Sheldon if he fell asleep, but that didn't happen earlier. Sheldon has a hard time dealing with the fame and attention from his colleagues and reporters. Then after Raj gives Amy a makeover he runs off with Penny to The Cheesecake Factory cursed by all the changes. Penny reminds him how much he's changed in the last twelve years and that the fact of change is really the constant. Sheldon accepts that.
In "The Stockholm Syndrome", Leonard and Penny are keeping a secret that she is expecting. When Penny returned from drinking with Sheldon at The Cheesecake Factory, they hopped into bed without "wrapping" something. Penny seems happy, but is unsure about the whole baby thing, while Leonard is ecstatic that he's going to be a father. Sheldon and Amy pay for their clothes, ticket and hotels so they can all attend the Nobel Prize ceremony. Sheldon notices that Penny was quite sick on the plane, so the secret comes out and he is just glad he won't get sick. Leonard is mad that Sheldon doesn't congratulate them and the Hofstadter's say they are heading home. Penny is very sick and claims that she can't travel and has to be there for Amy, with Leonard doing the same for Sheldon. At the ceremony, Sheldon puts aside his self-centered speech and realizes that his achievement isn't just his, but also his family and friends who encouraged him and tolerated him. Sheldon introduces his friends to the world and tells him how much he loves them.
==Trivia==
*Sheldon has more popularity than Leonard with the fans; however, in his world, people like him more than they like Sheldon, which is understandable considering their personalities.
**Leonard was originally the show's main protagonist before shifting to Sheldon.
*Leonard wants to achieve a Nobel Prize someday.
*Leonard is sceptical of loop quantum gravity.
*While Leonard's IQ is never directly stated in the show, he states in the "Pilot" that he and Sheldon have a combined IQ of 360. Sheldon states that his IQ is 187, so therefore Leonard must have an IQ of 173. Sheldon also states his intellect cannot be accurately measured by a "regular" IQ test. 
*Leonard received his PhD at age 24.
*Leonard is 5 ft. 5 in. (1.65 m) tall – the height of Johnny Galecki. In "The Egg Salad Equivalency", Sheldon states his "short, bespectacled colleague" is "... strutting around like he’s five-foot-six," which implies that Leonard is shorter than this measurement.
**Despite being short, Leonard states he is "too tall to be a jockey" (Though to Sheldon's amusement he's the perfect person for the sport).
**Leonard is a quarter-inch taller than Howard.
**By later seasons, Leonard's height doesn't appear to be too much of an issue for him anymore, given that he's now been shown to be taller than Amy, and roughly the same height as Penny.
*In "The Alien Parasite Hypothesis", which aired in 2010, Leonard says, "12 years after high school, and I’m still at the nerd table." This fact implies he was born in 1980, the same year as Sheldon, provided the following assumption that he graduated at the usual age of 18-years-old is supported by him having had a senior prom, which is mentioned in "The Peanut Reaction".
*Leonard has a grandmother with Alzheimer's that came to Thanksgiving and stripped naked, carving the turkey prior to the pilot.
*Leonard wears boxer shorts rather than underpants or trunks.
*Leonard always wears neutral-coloured sweat jackets.
*Despite his lactose-intolerance; however, Leonard can actually process small amounts of non-fat ice-cream without farting (according to Sheldon).
*Leonard has Darth Vader 'No More Tears' shampoo and Luke Skywalker hair conditioner.
*Leonard is a huge Superman fan, so much so that he owns all of the Superman films and more than 2600 Superman comics, as well as Superman underwear. He also has an unseen Superman costume with new boots that adds three inches to his height, which he wore at the comic book store's annual New Year's Eve party when the group went as the Justice League. Sheldon says he is their weak point, and he got replaced by Penny's friend Zack at a later party.
*Many of Leonard's shirts are scientifically inspired, such as in episode 1x03 where he can be seen wearing a shirt with a "Paradox" molecule.
*Leonard and Sheldon own Dell XPS computers. After "The Bozeman Reaction," he owned a Dell Adamo XPS.
*Leonard's favourite TV shows are Babylon 5 and Buffy the Vampire Slayer
*Leonard can play the cello, mirroring Johnny Galecki's own talent of playing the instrument.
**Leonard used to get stuffed in his own cello case.
*Leonard and Sheldon are named after actor and producer Sheldon Leonard.
*Leonard is unaccustomed to observing birthdays, by choice of his mother's views on psychiatry. He had never had a birthday party before moving to Pasadena.
*Leonard's parents both formerly lived in New Jersey. His father now lives in New York after his divorce.
*Leonard drove a silver Volkswagen Touareg with a luggage rack on top early on in the show.
*Leonard plays lead guitar on Rock Band.
*Leonard plays Age of Conan with the guys and is probably an Assassin (his character can be seen when he is checking on Penny via the game).
*Leonard has sleep apnea.
*Leonard gets carsick unless he sits in the front.
*Leonard has trouble making eye contact, only being able to do so with Penny and the rest of his friends, which could be indicative of Asperger's Syndrome, ADD, or simply social anxiety.
*Leonard is the group's (not including Penny) Wii bowling 'Team Captain'.
*Leonard's last name (Hofstadter) is in honour of Nobel Prize-Winning Physicist Robert Hofstadter, who worked at {{w|Stanford University in the field of Nuclear Physics.
*Leonard dislikes his name since it has "Nerd" in it, saying he prefers the name Angelo as it has "angel" and "Jello" in it, although he was high at the time.
*Leonard claimed he could hear Penny flushing her toilet from his apartment.
*Leonard tried to get the nickname "Duncan" by carrying around a Duncan brand yo-yo. This only resulted in bullies stealing the yo-yo and stuffing their socks into his mouth, making him "Sockmouth".
*Leonard was his school's debate club president.
*Leonard believes he is the "King of foreplay", as he used to do lengthy shows for Penny before they had sex.
*Leonard gets asthma attacks when he has panic attacks.
*He is the only male main character who wear glasses.
**Leonard tried wearing contacts in 7th grade, but could never get used to them.
**Leonard wears black-framed glasses (he originally wore tortoiseshell glasses eight years ago), even if in costume.
*He is the only character who has had five girlfriends Joyce Kim, Leslie Winkle, Penny, Stephanie Barnett and Priya Koothrappali), followed by Howard with four girlfriends (Christy Vanderbel, Leslie Winkle (friends with benefits), Lisa and Bernadette Rostenkowski) unless there are others that are not referred to.
*He is afraid of horses.
*Leonard always wears shorts when he goes to Kurt's apartment for Penny's errands.
*Leonard is usually wearing a t-shirt when he is in bed with Penny though not the first time.
**Also, until "The Colonization Application", he kept his socks on.
*Like Sheldon, Penny, Rajesh, and Amy, Leonard became a reverend to marry Howard and Bernadette.
*Bernadette, Raj, Leonard, Penny and Amy are the only members of the social group/main cast whose parents have both been seen on-camera - Sheldon's father died when Sheldon was a child, Howard's father abandoned him and his mother when Howard was eleven, Stuart's mother and father have been mentioned and are both alive, Emily's father has been mentioned and it is not known if he is dead or alive and there has been no appearance or mention of Emily's mother or Leslie's mother and father to date.
*Leonard's great-great-grandmother was half-Cherokee (as stated in "The Irish Pub Formulation"). This statement makes Leonard 1/32nd Cherokee.
*Estimated by Howard; Leonard's ideal mate is a short, low self-esteemed woman scientist living in a government facility in
*Throughout his childhood, his mother constantly conducted tests on him.
*As he stated in "The Contractual Obligation Implementation," when he was in middle school he wanted to be a rap star like Soop Dogg, but with "healthy respect for the police." He states his parents pushed him into becoming a scientist.
**Though, after watching Professor Proton, he eventually became inspired to follow through with science.
*One of Leonard's favourite fictional characters is Frodo Baggins from "The Lord of the Rings" (as stated by Sheldon in "The Large Hadron Collision").
*Leonard finds himself dating a married woman in "The Thanksgiving Decoupling".
**In Season 11, Raj would end up doing the same thing.
*The final proposal count to each other was Penny 3; Leonard 3.
*It has been suggested that the character of Leonard Hofstadter owes something to that of Professor Ponder Stibbons, a Research Wizard in Sir Terry Pratchett's Discworld series of fantasy novels. Ponder, in a university of Wizards devoted to magic, takes a minority view that Science is also important; he is to all intents and purposes a physicist. Leonard is a research physicist who enjoys fantasy works and plays games where he role-plays a Wizard. (Mystic Warlords of Ka'a). Both are geeky young men with glasses who affect clothing which is shapeless, baggy, neutrally coloured and for preference has a hood. The Science of Discworld series, which are co-written with eminent British scientists who are well known in USA academia, use Pratchett's fantasy world as a means of explaining ongoing scientific thought to a lay audience. The Discworld story begins with a massive explosion of magical energy that has to be diverted down a safe path, in order to avert a seriously Big Bang. Ponder Stibbons discovers he has inadvertently created a whole Universe out of nothing. This cools and expands and passes through stages like drooling autotrophs (explicitly referenced) until, presumably, California and Caltech evolve. It is possible Terry Pratchett watches and enjoys TBBT, and/or that Chuck Lorre reads Discworld novels.
*Leonard's relationship with Penny is the only one on the show that isn't set up by someone. Howard and Bernadette were set up by Penny, Sheldon and Amy were set up by Howard and Raj through a dating website, and Raj met Emily on a dating site. Stuart actually hired met his girlfriend and assistant, Denise, to work in his store.
*Leonard and Sheldon are similar to the characters of "The Odd Couple". Leonard Hofstadter is similar to Oscar Madison. Leonard may not be a slob, but he is fun-loving and nice. He is really cool and childlike.
*Leonard would just settle for being nominated for a Nobel Prize.
*Sheldon and Leonard drive up to Skywalker Ranch to see if they could get in. When they can't, Sheldon runs through the gate and almost gets the two of them arrested for trespassing. Despite not actually running with Sheldon, Leonard is permanently banned from Skywalker Ranch along with Sheldon and will be arrested if he ever comes back.
*Leonard, Sheldon, Howard and Raj are the only characters of the current main cast who have appeared in every episode. If the unaired pilot counts, then only Leonard and Sheldon appear in all episodes.
*Leonard is right-handed.
*Before the episode "The Peanut Reaction", Leonard had never had a birthday party.
*Leonard's iPad password is his birthday, specifically 4 digits the month and day, according to him, and since Leonard's birthday is known for being May 17, that would make his iPad password 0517.
**Despite the fact that Leonard's password for everything is "Kal-el", according to Sheldon.
*Leonard's go-to when he's in bed with a girl is "I'm sorry."
*In the episode "The Staircase Implementation", Leonard states that with Star Trek he prefers the original series over the next generation, but he prefers Picard over Kirk.
*He nicknamed his genitals "Alvin and the Chipmunks".
*It's strongly implied that Leonard resents Zack.
*He drives a Silver Saab Sedan 2002
*His life would be ruined if it wasn't for Sheldon as he could end up in jail for leaking confidential information to Joyce Kim or lost his life from his rocket fuel experiment.
*Leonard shares some similarities with fictional character Sherlock Holmes in that while they are both geniuses, they are also the least intelligent person in their respective families. Also, they are both the middle child and have one brother and one sister.
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