From the very first episode of The Big Bang Theory, we've see the connection between Leonard and Penny grow from platonic neighbors to husband and wife. Leonard has always had heart-shaped eyes for Penny, it just took Penny a couple of years to realize that she was good enough for Leonard, despite her insecurities.

We've seen this pair go from strangers to neighbors to lovers to exes to lovers again to husband and wife. They've been through it all and their best friends have been a part of the romance from the beginning.

Penny was "different" from the Leonard, Sheldon, Raj, and Howard but she soon became an important member of their friend group. She and Leonard have always been the closest and have done some pretty remarkable things for each other throughout the years. Let's take a look at 10 of them below.

LEONARD BOUGHT HER A CAR

Leonard and Penny arguing on The Big Bang Theory.

In the episode "The Friendship Turbulence," we see Penny quit her job as a waitress at the Cheesecake Factory to focus on making her career as an actress payoff. Leonard supported her on her journey even though he thought it was foolish to leave a paying gig.

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As Penny is transporting back and forth for auditions, her car breaks down. With no way to get anywhere and no money to fix her car, she fears she'll never make it as an actress and will have to waitress forever. To show how much Leonard loved and supported Penny, he bought her a car so she can get to and from auditions safely. It was a really tender moment between the two.

AND PENNY PAID LEONARD BACK AFTER HE BOUGHT HER THE CAR

Once Leonard and Penny are married, she soon starts working as a pharmaceutical sales rep for the same company Bernadette works for. It took some time but Penny soon began getting really good at her job and started bringing in the dough. As a way to say thank you, she sold her car (because her new job gave her a car to use) and gave the money directly to Leonard. Paying Leonard back pulled a weight off her chest but it made Leonard feel a little uncomfortable. To make it even, the two put the money in a joint account that would go towards their future together. Penny paying Leonard back proves how far she's come from that 22-year-old she was when they first met.

LEONARD WENT TO HER EX-BOYFRIEND'S PLACE TO GET HER MONEY BACK

Leonard at Penny's ex-boyfriend's house on TBBT

Leonard has proven time and time again that he would do anything for Penny. When she first moved in, he went to her ex-boyfriend's place to get her TV back after they broke up. Her ex-boyfriend was massive and could have crushed little Leonard and his friends but he did it anyway.

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Years later, the same boyfriend borrowed $1,800 from Penny and never paid her back. Without that money, Penny couldn't pay her bills and sat in a dark apartment until he finally paid her back (thanks to the help of Leonard).

PENNY THREW LEONARD HIS FIRST BIRTHDAY PARTY

In the first season, Penny learns that Leonard never had a birthday party. His parents didn't think being born was an accomplishment, so why would they throw a party? Whenever Leonard's birthday rolls around, he continues the day as if it were any other.

Penny wanted Leonard to feel loved and to know what a real birthday party was like, so she decided to plan a surprise party for him. Due to Howard's allergic reaction to nuts, however, Leonard missed his own birthday party but it was the thought that counts on Penny's behalf.

LEONARD BROUGHT HER A SNOWFLAKE FROM THE NORTH POLE

Penny and Leonard weren't even dating when Leonard brought back a snowflake from the North Pole. Granted, the two started seeing each other the day he got back to Pasadena but it proves how much Penny was on his mind. Considering snowflakes are one of a kind, it's truly romantic that Leonard found a way to preserve one and brought it home for her.

PENNY HAS A COLLECTION OF ALL THE MEMORIES SHE'S SHARED WITH LEONARD

Penny and Leonard kissing in The Big Bang Theory.

Penny has been with a lot of men but she hasn't been in long, fulfilling relationships with them. Leonard is the first man that sparks her intellectually and challenges her.

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Knowing how romantic and loving Leonard is (and always has been), Penny tried her hardest to give him a good gift but it fell flat. The book she bought him was a book he already had. But the mood changes when Leonard realizes Penny has saved everything memorable from their relationship. Knowing she does this in private was enough to make Leonard feel loved in return.

LEONARD TRIES TO HELP PENNY WITH COLLEGE

Penny and Leonard argue about college on TBBT

As a community school dropout, Penny felt intimidated when she and Leonard first began dating. She didn't have a fancy degree like the rest of the guys had and didn't have much to add to dinner conversation. Down the line when she and Leonard are more serious, Penny decides to take a few classes at the community college until she knows what she wants to do with her life. Leonard was ecstatic for Penny for deciding to do this on her own but after reading her first essay... He knew he could help her do better. Penny didn't love the fact that Leonard took over her essay and tried making it better but it came from a good place!

PENNY PICKS HIS MOM UP FROM THE AIRPORT

Leonard always mentioned that his mom and dad were cold, unloving people. They were very science-based and adored his siblings more for their high accomplishments. Penny meets Beverly when she and Leonard are just friends, which broke the ice in a gentle way.

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But when she and Leonard begin dating, she helps Leonard's anxiety by spending more time with her. She even picked her up from the airport so Leonard didn't have to deal with her, which was a huge relief for Leonard.

LEONARD WAITING UNTIL PENNY WAS READY TO GET MARRIED (AND PROPOSING WITH A RING)

Leonard proposes to Penny on The Big Bang Theory

When Penny and Leonard get more serious (with fewer breakups), they joked about getting engaged a few times. Penny even got drunk one night and proposed to Leonard because he was a safe choice and she was going through a hard time. Leonard, however, was unimpressed and turned down her proposal. The two went back and forth about the whole engagement thing until it was finally time. Penny seemed to be ready for the next step and that's when Leonard got down on one knee and gave her a ring. Penny was stunned by the fact that Leonard had a ring in his wallet all this time and it really made the moment special.

PENNY GETS LEONARD TO DO HIS GRADUATION COMMENCEMENT SPEECH

Leonard in his graduation outfit via Skype on TBBT

When you sit back and realize that Penny has never been to Leonard's hometown before (and the same for Leonard), it makes you wonder why not? In "The Graduation Transmission," Penny is finally flying to New Jersey to watch Leonard give a commencement speech to his former high school. After a bad snowstorm hits New Jersey though, all flights from California are canceled and he can't make it. Penny realized what a big deal this was and how much Leonard wanted to do it so she set up a way to do the speech via Skype. She even got him a graduation gown to pull the good deed all together!

NEXT: The Big Bang Theory: Penny's 5 Best Outfits (& 5 Worst)