A heartfelt speech, a somber agreement, a prank involving zombies — it’s moments
like these that make The Big Bang Theory legendary, even years after its final wrap.
These are the show’s biggest moments ranked from good to best!
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 Season 3's "The Staircase Implementation" when he tells
Penny the story of how he became Sheldon's roommate.
When Leonard started his job as a researcher at Caltech, he needed to rent an apartment
nearby.
He met Sheldon 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 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, played by Simon Helberg, and Raj, played by
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.
Leonard felt indebted to Sheldon, and the two quickly became good friends thereafter.
"You're welcome."
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 in, the agreement contains elaborate rules for
the code of conduct between him and Sheldon as roommates and friends.
Naturally, the agreement is heavily skewed in Sheldon's favor.
But Leonard's one-time girlfriend Priya, played by Aarti Mann, isn't so easily controlled
by the paradigms of the agreement.
Priya's a lawyer and doesn't appreciate the way Sheldon rigged the agreement to give himself
power over Leonard.
In "The Agreement Dissection" in Season 4, Priya argues around the clauses in the contract,
much to Leonard's delight.
Sheldon then threatens to expose Priya's relationship with Leonard to her disapproving parents if
the original terms of the 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.
And it usually falls on Leonard to keep Sheldon in line during his most eccentric moments.
One of the biggest instances of this occurs in Season 3 with "The Einstein Approximation,"
in which Sheldon has 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 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, this
often becomes a sore spot for Leonard's friends, who think he's being taken advantage of.
Leonard has a major reckoning in the Season 5 episode "The Friendship Contraction."
"You know what?
I'm sick of the roommate agreement."
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.
At first, Sheldon tries to replace Leonard with his other friends, but it quickly becomes
apparent that no one has the patience to deal with him.
Desperate to have Leonard back but loath 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."
"We set aside a day to celebrate all your contributions to my life, both actual and
imagined by you."
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"
in Season 7 when Leonard reveals that a forgotten DVD they'd once rented is seven years overdue.
He makes a deal with Leonard whereby he must wear an extremely itchy sweater under his
clothes until he manages to return the DVD 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.
In the end, it's revealed that Sheldon had paid for the DVD years ago and was using the
situation to teach Leonard a lesson about 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 lives, as he amply demonstrates in Season 3 with
"The Large Hadron Collision."
When Leonard gets the opportunity to go to Switzerland to observe the Large Hadron Collider,
he's thrilled to be able to take his girlfriend, Penny, with him to celebrate Valentine's Day.
When Sheldon hears about Leonard's trip, however, he assumes his roommate would take him instead
of Penny.
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.
If there's one character in "The Big Bang Theory" who seems incapable of changing, it's
Sheldon Cooper, who's perennially convinced that any problem is with everyone else, not
him.
Incredibly, however, Sheldon does begin to change after meeting Amy Farrah Fowler played
by Mayim Bialik.
Although he's completely uninterested in romance at first, Sheldon begins to date Amy as a
sort of experiment.
He repeatedly insists they aren't romantically involved, but over time, Sheldon begins to
realize 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 Season 5's "The Pulled Groin
Extrapolation."
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 and karate-chops him.
"Why'd you do that?"
"To send a message.
She is not for you!"
The joy of Sheldon's characterization is in watching someone with 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 for a perfect storm of hilarity in "The Bozeman Reaction" in Season
3.
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 decides to relocate to a place where there would be less chance of getting
murdered.
"Is he quitting his job at the University?"
"Oh, no, he's going to telecommute.
Everybody's really excited about it."
Throughout the ordeal, Leonard repeatedly tries to reassure Sheldon that he's safe in
their apartment, 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.
It's much rarer to see Sheldon taking care of Leonard.
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 Season 6's "The Decoupling Fluctuation."
While Leonard and Penny are dating, it's revealed that Penny has secret doubts about their relationship.
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 drops his usual
arrogance and aloofness, and instead has a marked humility that he reserves for only
the most special of occasions.
"Please don't hurt my friend."
After many years as Sheldon's roommate, Leonard had gathered a vast collection of knowledge
about his friend.
Some of that knowledge is actively uncomfortable, like 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" in Season 2.
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.
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 hostile, it kickstarts an escalating series of pranks
between her and Sheldon that soon threatens to spill over into violence.
That's when Leonard tells 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 forces Sheldon to apologize.
Leonard and Sheldon can often come across as immature and ill-equipped to handle adult
life.
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" in
Season 1.
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.
An indignant Leonard declares 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, 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 quirks is his hypochondria, which is aggravated by his genius intellect.
He often envisions worst-case scenarios whenever he has to undergo any sort of medical procedure.
In the Season 8 episode, "The Septum Deviation," Sheldon's worries transfer over to Leonard.
After a routine checkup, Leonard learns 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.
All through the episode, Sheldon remains extremely panicky over his friend's surgery.
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.
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 Season 5's "The Good Guy Fluctuation."
While working late in his office, 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, and he plots his revenge against the others.
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 make the pranks fail.
Finally, while Leonard is alone in their apartment musing over some devastating news, 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 win the Nobel Prize for physics.
The big day finally arrives in the series finale, "The Stockholm Syndrome."
Sheldon and Amy win a joint Nobel for their research in super asymmetry.
On the stage after receiving his award, Sheldon looks over at Leonard and his 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 thank his friends for helping him grow as
a person and as a scientist.
He calls each one and asks them to stand, then in his most honest moment on the show,
says,
"I apologize if I haven't been the friend you deserve."
"But I want you to know, in my way, I love you all."
With that speech, Sheldon goes from man-child to mature adult and acknowledges the almost
superhuman patience that Leonard and the others had displayed toward him over the years.
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