The Most Iconic Big Bang Theory Roommate Moments Ranked

From 2007 to 2019, "The Big Bang Theory" told the story of a group of brilliant scientists who also happened to be hardcore nerds. One day, they find their peaceful lives of scientific research and geek culture turned upside down by the arrival of a new girl next door named Penny (Kaley Cuoco), who forces the guys to step outside their comfort zones.

Chief among the main characters on the show are roommates Leonard Hofstadter (Johnny Galecki) and Sheldon Cooper (Jim Parsons). Both are brilliant scientists, but they each have very different perspectives on life. Leonard wants to spend more time with Penny and expand his social circle, while Sheldon looks down on the rest of humanity and believes himself to be happily self-sufficient.

The relationship between Leonard and Sheldon as friends and roommates is one of the cornerstones of "The Big Bang Theory." And over the course of the show, that relationship yields some hilarious bits. After years of living together, Leonard and Sheldon eventually move in with their respective romantic partners, but their importance in each other's lives doesn't change. Here are some of the best roommate moments between Leonard and Sheldon in "The Big Bang Theory."      

In the early seasons of "The Big Bang Theory," it's easy to wonder why Leonard lives with Sheldon in the first place, given how difficult he can be. Leonard answers this question in "The Staircase Implementation" (Season 3, Episode 22) when he tells Penny the story of how he became Sheldon's roommate.

When Leonard was just starting his job as a researcher at Caltech, he needed to rent an apartment nearby. He met Sheldon for the first time when the latter was sub-letting his apartment, as his previous roommate Sebastian could no longer stand to live with him. At that time, Sheldon was particularly difficult, and he made Leonard answer a bunch of ridiculous questions before reluctantly allowing him to move in.

The two didn't get along at first, and Leonard avoided having to hang out with Sheldon, preferring instead to conduct home experiments with Howard (Simon Helberg) and Raj (Kunal Nayyar). But one such experiment quickly turned dangerous when the rocket fuel Leonard had created started malfunctioning. It was Sheldon's quick thinking that prevented the fuel from exploding in their apartment (it blew up their building's elevator instead). Leonard felt indebted to Sheldon, and the two quickly became good friends thereafter.

The most important way in which Sheldon retains power in his friendship with Leonard is through the elaborate "Roommate Agreement." Signed by Leonard when he first moved into the apartment, the agreement contains elaborate rules for the code of conduct between him and Sheldon as both roommates and friends. 

Naturally, Sheldon being Sheldon, the agreement is heavily skewed in his favor — an arrangement that the exasperated Leonard is usually too fed-up with to argue against. But Leonard's one-time girlfriend Priya (Aarti Mann) isn't so easily controlled by the paradigms of the Roommate Agreement. Priya's a lawyer, and she doesn't appreciate the way Sheldon rigged the agreement to give himself power over Leonard. In "The Agreement Dissection" (Season 4, Episode 21), Priya manages to successfully argue around the clauses in the contract using her professional knowledge, much to Leonard's delight and Sheldon's bafflement. Sheldon is dangerous when backed into a corner, however, and he proves that by threatening to expose Priya's relationship with Leonard to her disapproving parents if the original terms of the Roommate Agreement aren't reinstated. At Priya's urging, Leonard concedes to Sheldon's demands, leaving him once again the ruler of their little apartment kingdom.    

Sheldon never shows much interest in following the dictates of conventional society. His genius intellect and antisocial nature often combine to create a perfect storm of insufferable behavior. As his best friend/roommate/long-suffering caretaker, it usually falls on Leonard to keep Sheldon in line during his most eccentric moments.

One of the biggest instances of this aspect of their relationship occurs in "The Einstein Approximation" (Season 3, Episode 14). For the longest time, Sheldon had been stuck on a problem at work regarding the behavior of electrons. This leads him to try increasingly bizarre ways to wrap his brain around the issue while forgoing the usual, pesky human weaknesses of food and sleep. 

It's left to Leonard to try to keep a handle on the sleep-deprived lunatic that his roommate becomes. Sheldon works all night on a whiteboard trying unsuccessfully to solve his problem, which he promptly tosses into the street the next morning, causing a car crash. Sheldon also lays out intricate patterns of marbles in the living room in a bid to understand the movement of electrons, which causes Penny and Leonard to slip and fall painfully. His crowning moment, however, is when Leonard is forced to follow Sheldon into a kid's ball pit that the latter swims around in like Scrooge McDuck, shouting "Bazinga!" repeatedly.   

Though Leonard is devoted to taking care of Sheldon like an older brother would, Sheldon constantly denies the idea that he needs someone to look after him, and he generally ignores all that Leonard does on his behalf. This often becomes a sore spot for Leonard's friends, who think he's being taken advantage of.

Leonard himself comes to realize this at different points in the show, with a major reckoning occurring in "The Friendship Contraction" (Season 5, Episode 15). After a long day of Sheldon being his usual demanding self, Leonard invokes Clause 209 of the Roommate Agreement, nullifying the "friendship" aspect of their relationship and reducing them to mere roommates with no personal obligations to each other. At first, Sheldon tries to replace Leonard with his other friends, but it quickly becomes apparent that no one else has the patience to deal with his outrageous demands. Desperate to have Leonard back as a friend but loathe to admit defeat, Sheldon resorts to turning off the entire building's lights in an effort to make Leonard need his help, but the ruse doesn't work. Finally, Leonard agrees to reinstate the "friendship" clause in return for an annual "Leonard's Day," which, as Sheldon puts it, will be a day to "celebrate all [of Leonard's] contributions to [Sheldon's] life, both actual and imagined."     

One of the most accurate descriptions of Sheldon Cooper is provided by Leonard when he tells Penny, "The guy's one lab accident away from being a supervillain." Sheldon's Machiavellian tendencies are on full display in "The Itchy Brain Simulation" (Season 7, Episode 8) when Leonard reveals that a forgotten DVD they'd once rented is seven years overdue. 

At first, Leonard fears a furious outburst from Sheldon over the issue, but he remains uncharacteristically nonchalant. He makes a deal with Leonard whereby he must wear an extremely itchy sweater under his clothes until he manages to return the DVD, just so he can appreciate how uncomfortable Sheldon feels mentally whenever he's forced to deal with unfinished business. 

Leonard agrees to the deal, and the rest of the episode sees him growing increasingly desperate as he continues to wear the sweater while trying to find a way to return the DVD to its rightful owner. In the end, it's revealed that the reason Sheldon didn't get upset was that he'd returned the real DVD years ago, and he was just using the situation to teach Leonard a lesson about personal responsibility. The angry red welts on Leonard's body caused by the sweater at the end of the episode show just how painful that lesson is. 

Sheldon's primary character trait throughout most of "The Big Bang Theory" is his overwhelming narcissism. He's the most important person in his life, and he expects his friends to place him in a similarly important position in their own lives, as he amply demonstrates in "The Large Hadron Collision" (Season 3, Episode 15).

Leonard had finally started dating Penny, so when he gets the opportunity to go to Switzerland to observe the Large Hadron Collider, he's thrilled to be able to take her with him to celebrate Valentine's Day. Sheldon also hears about Leonard's trip, however, and he automatically assumes his roommate would take him to see the Hadron Collider instead of his girlfriend. When he discovers that's not the case, he's outraged. Throughout the episode, Sheldon begs, pleads, and schemes his way around convincing Leonard to take him to Switzerland instead of Penny. The incident is a great example of both Sheldon's inability to pick up on social cues and his exaggerated sense of entitlement, particularly when it comes to Leonard.    

If there's one character in "The Big Bang Theory" who seems incapable of changing at the start of the series, it's Sheldon Cooper. While the other characters often acknowledge their shortcomings, Sheldon is perennially convinced that the problem is with everyone else, not him. He believes that the world needs to change around him rather than him needing to change to fit into it. 

Incredibly, however, Sheldon does begin to change after meeting Amy Farrah Fowler (Mayim Bialik). Although he's completely uninterested in romance at the start, Sheldon begins to date Amy as a sort of experiment. He repeatedly insists that he and Amy aren't romantically involved, and he denies that he'd ever need romance in his life, but over time, Sheldon begins to realize that he cares a great deal more for Amy than he was initially prepared to admit. One of the earliest and most hilarious examples of this occurs in "The Pulled Groin Extrapolation" (Season 5, Episode 3). At first, Sheldon seems completely indifferent to the fact that Leonard and Amy had gone to a party together — until he misconstrues something Leonard says as a hint that they'd gotten frisky. In response, Sheldon karate-chops his roommate and heatedly declares that "She is not for you!" 

The joy of Sheldon's characterization is in watching someone with a genius intellect inhabit the body of a hyperactive man-child. He has no sense of social niceties, and Leonard always acts as his reluctant caretaker. All those factors combine to create the perfect storm of hilarity in "The Bozeman Reaction" (Season 3, Episode 13).

After a night out, Leonard and Sheldon arrive back at their apartment to discover that the lock has been broken and their belongings have been ransacked. Although the robbers didn't take anything of material value, Sheldon becomes paranoid at the thought of another possible break-in. Throughout the episode, he comes up with increasingly elaborate anti-burglary alarms that end up backfiring hilariously.

Finally, Sheldon is forced to conclude that he can no longer live in a city that's a cesspool of crime, and he decides to relocate to a place where there would be less chance of getting murdered in his sleep. Throughout the ordeal, Leonard repeatedly tries to reassure Sheldon that he's safe in their apartment. He shows the full extent of his care for Sheldon by putting up with all of his hysterics and ridiculous schemes.  

We often see Leonard taking care of Sheldon and making concessions for his off-putting behavior, to the extent that Leonard almost comes across as a doormat in their relationship. It's much rarer to see Sheldon taking care of Leonard since he generally treats the latter as his sidekick. 

But the truth is, despite taking his friendship for granted most of the time, Sheldon does genuinely care for Leonard. The sweetest example of his affection occurs in "The Decoupling Fluctuation" (Season 6, Episode 2). While Leonard and Penny are dating, it's revealed that Penny has secret doubts about their relationship and isn't even sure she'll be with Leonard for long. When Sheldon learns of this, he becomes increasingly agitated with the weight of the secret and its potential impact on his friend. This tension causes Sheldon to wake Penny up in the middle of the night to tell her all the ways Leonard is a great guy and prime boyfriend material. As the thoroughly exasperated Penny orders Sheldon to leave, he finally tells her, "Please don't hurt my friend," with no hint of his usual arrogance or aloofness, and with a marked humility that he reserves for only the most special of occasions.  

After many years as Sheldon's roommate, Leonard had gathered a vast collection of knowledge about his friend. Much of that knowledge is completely useless, and some of it is actively uncomfortable, like intimately (and unwillingly) knowing Sheldon's bathroom schedule. But sometimes, Leonard's expert knowledge of Sheldon's personal life proves invaluable. 

Take the case of "The Panty Piñata Polarization" (Season 2, Episode 7). After a long day of having to deal with Sheldon's nonsense, Penny finally puts her foot down and declares she will no longer follow his rules for the apartment. This results in Penny being "banished" until she's willing to apologize and take a class to improve her attitude. When Penny proves unrepentant and actively hostile, it kickstarts an escalating series of pranks between her and Sheldon that soon threatens to spill over into violence. That's when Leonard reveals to Penny that he knows Sheldon's kryptonite. He gives her the phone number of Sheldon's mother, Mary, who swiftly puts an end to the war and even forces Sheldon to apologize. In the end, Sheldon can only muse in baffled fury over who could have given Penny his mom's number while Leonard quietly smirks in the background. 

Leonard and Sheldon can often come across as immature and ill-equipped to handle adult life, and that's generally a fair assessment of their personalities. But the fact remains that both are also top researchers in their fields whose professional reputations are quite distinguished. 

These two factors collide in an epic manner in "The Cooper-Hofstadter Polarization" (Season 1, Episode 9). Leonard and Sheldon write a research paper together and are subsequently invited to present it at a conference in front of their peers. Sheldon doesn't want to go because he doesn't think the crowd at the conference has the necessary genius to properly appreciate his work. In response, an indignant Leonard declares that he'll be going to the conference with or without his co-author. 

Sheldon refuses to allow Leonard to present the paper alone and also refuses to accompany him. A long, petty fight ensues between the two friends, culminating in them airing out their dirty laundry in front of the audience at the conference. Sheldon attempts to blow Leonard's brain apart using his mind, which obviously doesn't work. The whole ordeal later gets put up on the internet as a lasting testament to Leonard and Sheldon's bizarre relationship. 

One of Sheldon's many, many peccadilloes is his penchant for bursts of hypochondria, which are aggravated by his genius intellect. He often envisions the worst possible scenarios whenever he has to undergo any sort of medical procedure or spend an extended amount of time in a hospital. In "The Septum Deviation" (Season 8, Episode 9), Sheldon's worries transfer over to Leonard.

After a routine checkup, Leonard learns that he has a deviated septum that prevents him from breathing properly. He decides to get a small surgery to correct his condition, but Sheldon is appalled, believing that it could lead to all sorts of complications if anything were to go even slightly wrong. All through the episode, Sheldon remains extremely panicky over his friend's surgery, even though Leonard himself isn't too worried. Things come to a head when the light goes out in the middle of the operation, causing Sheldon to run screaming into the room to try to save Leonard and subsequently crash into a glass door, breaking his nose. In an odd way, it's one of the sweetest things Sheldon ever does for Leonard.  

To the rest of the world, Sheldon Cooper might seem like a humorless man who takes himself way too seriously. But his closest friends know that Sheldon has an impish sense of humor, and that he's more than willing to participate in all kinds of hijinks with the right companions. One of the most entertaining instances of this occurs in "The Good Guy Fluctuation" (Season 5, Episode 7).

While working late in his office one day, Sheldon is beset by a series of pranks by Raj and Howard. Sheldon manages to see through all of them with his trademark air of superiority, only to end up completely freaking out when Leonard sneaks up behind him in a scary mask. The incident leaves a deep impression on Sheldon's mind, and he plots his revenge against the others for making him look like a fool.

All through the episode, Sheldon tries to play pranks on the others, but his lack of social awareness and the fact that the others know he's coming for them make all the pranks fail. Finally, while Leonard is sitting alone in their apartment musing over some devastating news he just learned about his girlfriend Priya, Sheldon pops up screaming from beneath his spot on their couch dressed in zombie makeup for an epically hilarious prank. 

Sheldon never tries to hide the fact that he considers himself superior to his friends. His dream since childhood was always to establish that superiority once and for all by winning the Nobel Prize for physics. He even daydreamed sometimes about how much self-praise he'd indulge in while making his speech for winning the award. 

The big day finally arrives in the "Big Bang Theory" series finale, "The Stockholm Syndrome." Sheldon and Amy win a joint Nobel for their research into super asymmetry. On the stage after receiving his award, preparing to make his speech, Sheldon looks over at Leonard and his other friends in the audience and realizes he's no longer the same man who years before dreamed only of bragging about his genius before the world.  

Instead, Sheldon takes the opportunity to name his friends and thank them for helping him grow, both as a person and as a scientist. "Howard, Bernadette, Raj, Penny, Leonard. I apologize if I haven't been the friend you deserve," Sheldon says in his most honest moment ever on the show, adding, "But I want you to know, in my way, I love you all." With that speech, Sheldon finally goes from man-child to mature adult and acknowledges the almost superhuman patience that Leonard and the others had displayed towards him over the years.