As the three main characters of The Big Bang Theory, we saw the fun-loving relationship between Sheldon, Leonard, and Penny. (Howard, Raj, Bernadette, and Amy were also main characters but the entire show had a soft spot for our favorite threesome.) And while the show was mainly about Sheldon's high IQ and how his friends tolerated his naivety to common sense, the Leonard and Penny storyline was a strong one.

RELATED: The Big Bang Theory: 10 Best Cameos In The Series

Viewers learned from the first episode that Leonard had strong feelings for Penny. The two of them being neighbors really gave them a fighting chance in their relationship. From neighbors, they became friends, and that friendship soon grew into love. However, these two had their fair share of ups and downs throughout 12 seasons. Leonard may have done some incredibly nice things for Penny but he also hurt her many times. From the car that he bought her to the time he kissed another woman, here are five of the nicest (and rudest) things he's ever done to Penny.

HE BOUGHT HER A CAR WHEN SHE WAS GOING THROUGH A ROUGH TIME

When we first meet Penny, we learn that she's a struggling actress working at the local Cheesecake Factory to make ends meet. Leonard and co. have a feeling Penny isn't the strongest actress because she never landed anything concrete throughout all her years in Hollywood.

She eventually quits her job as a waitress to focus 100% of her time on acting. But when her car breaks down, so do her dreams. That is until Leonard steps up and buys Penny a car she can take to and from auditions to make her dream a reality.

HE HID A SECRET SAVINGS ACCOUNT FROM HER

In "The Big Bear Precipitation," Leonard and Penny go on a winter getaway to a cabin with Sheldon and Amy. As the foursome are playing a drinking game by the fire, Penny learns that Leonard has a secret savings account that he's never told her about.

Things get worse when he explains the reason he never told her is because she wasn't great with money. This is, of course, confirmed when she explains how much debt she's in. The two eventually come to an understanding but hiding finances from your spouse isn't necessarily a good thing, Leonard.

HE CONSTANTLY BOUGHT HER DINNER (EVEN WHEN THEY WEREN'T DATING)

In every Big Bang Theory episode, we see the gang huddled around Apartment 4A eating pizza, Chinese food, or some kind of takeout. It's a simple scene but it's often a fan's favorite.

RELATED: Big Bang Theory: Every Relationship Ranked (& How Long They Lasted)

When the two first met, Leonard asked Penny to join them for dinner. It was a casual way of meeting one another but fast forward 12 years later and he was still buying dinner for her. Through all their breakups and makeups, Leonard has only asked Penny for money a handful of times.

HE REWROTE HER COLLEGE ESSAY WITHOUT TELLING HER

As Penny and Leonard became more serious and Penny became more successful in her own right, she decided to take a few courses at the community college. She initially didn't tell Leonard because she feared he would be over-enthusiastic about her education, and that was exactly what happened.

As Penny slept, Leonard took a look at her essay and decided to *help* her by making her paper better (to his standards). Penny, of course, noticed and was infuriated that he didn't have enough trust or confidence in her own abilities.

HE SET UP HER PERFECT DATE NIGHT AT HOME ON THE COUCH

In "The Date Night Variable," Leonard mistakenly asked Penny to marry him while they were in bed together. To make up for his foolish timing, he decided to throw her perfect version of date night. He put on a game for her to watch, had a cold beer waiting for her, and had her favorite snacks on deck.

RELATED: Big Bang Theory: 10 Hidden Details About Sheldon And Leonard's Apartment

It was such a small gesture but it's sweet he went out of his way to make the perfect night for her, even though he didn't have one ounce of interest in any of the things mentioned.

HE MADE HER FEEL DUMB FOR GETTING MARRIED TO ZACK

Penny finds out she has been married to Zack on Thanksgiving on The Big Bang Theory

During one of Penny and Leonard's many breakups, she rebounded with a guy named Zack. Zack was, essentially, everything Leonard wasn't. He was tall and in shape but he was also very—for lack of a better word—dumb. Leonard was always fascinated by Zack's curiosity in science but never liked him since Penny had obviously been with him. However, when Penny and Leonard eventually do get back together, Leonard learns that Penny married Zack in Las Vegas.

Unbeknownst to Penny, she thought those Las Vegas weddings for fake... This enraged Leonard and he made her feel dumb for thinking her wedding was fake. But as we all know, his anger was an emotional response to Penny marrying Zach while turning down Leonard.

HE BROUGHT HER A SNOWFLAKE FROM THE NORTH POLE

Penny and Leonard's entire relationship changed when he went to the North Pole for three months to work on an experiment with Sheldon, Raj, and Howard. When he came back to California, he and Penny couldn't keep their hands off of each other.

He even brought her back a gift from the North Pole: a snowflake. Considering how rare snowflakes are, this was a gift she cherished.

HE MADE HER TAKE CARE OF SHELDON WHEN HE WAS SICK (AS HE WENT TO THE MOVIES)

Penny taking care of sick Sheldon on TBBT

The more fans got to know Sheldon, the more they understood why Leonard hid from him on special occasions. Now, we all love our Shelly but he's not the easier person to be around when he's sick. He's needy when he's healthy but it's a whole other ballgame when he's sick.

RELATED: Big Bang Theory: 10 Unanswered Questions We Still Have About The Main Characters

Knowing how clingy Sheldon is when he's ill, Leonard fled the apartment for the entire day and left Penny to take care of him. Penny eventually found Leonard and gave him a piece of her mind but it was still a selfish thing for him to do.

HE PRETENDED TO DATE HER AGAIN TO SAVE FACE FOR HER FATHER

During one of Penny and Leonard's many breakups, the two always stayed friends. Sure, times got weird for them (especially when they started dating other people), but there was always a genuine love there.

When Penny's dad came to visit her, however, she didn't have the heart to tell him that she and Leonard broke up (because he loved Leonard so much), so she practically forced Leonard to be her pretend boyfriend for the weekend. Leonard, of course, ate up the attention but knowing how much he really loved her, it had to take a lot for him to pretend to date her when he wished he still was.

HE CHEATED ON HER

Leonard eating lunch with Mandy at Caltech on TBBT

Not only did Leonard cheat on Penny while he was away at sea but he told her this on their spur of the moment wedding night!

It was shocking for fans to hear that Leonard was unfaithful because he was always the person in the relationship who didn't trust Penny. So for him to turn the tables and kiss someone else (while Penny never did) was totally uncalled for. Lucky for him, Penny forgave him but it was still an unjustifiable action.

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