The main characters of The Big Bang Theory have been through a lot over 12 seasons. In season 1, Sheldon, Leonard, Howard, and Raj were admitted nerds and had a deep appreciation for science and a love for women. Fast forward to the final season, most of the characters had long-term relationships and made valuable contributions to science and society.

This beloved group of friends has been through a lot together and transformed into different people by the series finale. However, the gang did not develop and grow at the same rate. Some character arcs were downright lackluster compared to others.

Updated on July 7th, 2022, by Lynn Gibbs: There was a lot that happened to the beloved friend group on The Big Bang Theory after 12 seasons. In season 1, each character had hopes and dreams for their future careers and relationships. As fans, it was fun to follow the characters on their journey of self-discovery. By the final season, Leonard, Sheldon, and co. had been through so much that it was humbling to be reminded of their growth. However, everyone's character arc wasn't as impressive as the next. Some declined in areas of their life while others surprised fans and thrived. 

Leonard Hofstadter Became Complacent

Leonard looking off camera in The Big Bang Theory

Compared to his friends, Leonard didn't grow much over 12 seasons. He was able to become a loyal and dedicated husband to a woman he desired the entire series but he let some aspects of his life slide. Unlike the rest of his friends, Leonard didn't make the same kinds of contributions to science that he originally wanted. He was a part of incredible projects but when comparing friends, Leonard was the least successful and seemed to lose his passion for science.

RELATED: Leonard & Penny's Relationship Timeline, Season By Season

Leonard whined a lot and became complacent. He was also jealous of Penny's success and didn't know how to handle her not needing him like she used to. His relationship timeline with Penny came more important to him than work. Leonard was a standup guy and a devoted friend but his character arc was the least compelling among his friends.

Bernadette Rostenkowski-Wolowitz Was Successful But Her Personality Took A Turn

Bernadette at the hospital with Howard, Raj, and Stuart on TBBT

When viewers met Bernadette, she was a shy woman with a high-pitched voice who laughed at Howard's jokes because it made him happy. But as time went on, it was obvious that she was incredibly right and more put-together than Howard was. Bernadette went on to get her Ph.D. before landing a profitable job in microbiology and later became a wife and a working mother of two.

While her profession was impressive, Bernadette's personality faded as her career took off. She became more judgmental and snarky to members of the group. One of the more annoying things about Bernadette was that she bossed Howard around, treated him like a kid when it came to finances, and even got into arguments with the women over differences of opinion. It was wonderful to see a successful woman in science but her personality took a dark turn.

Stuart's Luck Changed As The Series Continued

Big Bang Theory Stuart and friends in Howard's kitchen

Stuart Bloom didn't start as a main character but he might as well have been one by season 12. He was the owner of the comic book store that the gang went to weekly. However, Stuart suffered betrayals on TBBT from the group and it took time to become included. Stuart later became an important part of their inner circle.

He lacked financial security, was desperate, and hungry for most of the series but once he got his comic book store up and running after a fire, things turned around for him. His shop became popular after reopening, he started dating Denise, he was hanging out with the group more often, and he seemed to finally be financially stable. It was nice to see Stuart have a happy ending and a character arc that got better.

Raj Kootherpali Found Independence

Raj valentine's day

Raj was an underrated character. He was unable to speak to women because of his selective mutism, and it made it hard for him to socialize with his friends — especially when the gang befriended Penny. By the final season, Raj no longer needed alcohol to speak to women and was a confident man. He made extraordinary finds in science, like the space prob, comet, and possible alien life. He even started working part-time at the planetarium to further his love of science.

Outside of work, Raj decided to stop relying on his wealthy parents and started from the ground up to solidify himself as a self-made man. And while fans wanted him to end up with Anu, he showed tremendous character growth by calling off the wedding and focusing on himself.

Amy Farrah Fowler's Character Was Fleshed Out

Mayim Bialik as Amy Farrah Fowler in The Big Bang Theory

Fans didn't meet Amy until season 3, but she's one of the most transformative characters in the show. A neuroscientist, Amy started robotically and said exactly what she was thinking, even if it offended others; she was the female Sheldon.

RELATED: Sheldon & Amy's Relationship Timeline, Season By Season

By the series finale, Amy was no longer that distant woman fans met in season 1. She was a Nobel Prize winner, dear friend, and a loving wife in her relationship timeline with Sheldon. She learned to open up and trust others and have the life her younger self always dreamt of. It was fulfilling for fans to see Amy's character arc so full and fleshed out from her career to friendships to love life.

Penny Became Independent And Successful

penny walking into t he boys apartment - tbbt

Fans can't deny Penny's success story. She came to Los Angeles as a 21-year-old with hopes of being an actress. She waited tables at The Cheesecake Factory and barely got by financially. She dated jerks who took advantage of her and she didn't have any true friends... That is until she met Leonard and Sheldon.

By the finale, Penny was whole. She was married to her best friend, was an integral part of her friend group, and started a successful job in pharmaceutical sales. Penny was doing so well at work that Bernadette even promoted her. Penny was no longer the poor wishful thinker that she was in season 1. She was now a driven woman with a good head on her shoulders who didn't need to depend on anyone but herself.

Howard Wolowitz Had The Last Laugh

Howard going to space -TBBT

Howard Wolowitz's character arc was nothing short of a miracle. While he was one of the funniest members of the group, Howard also started as the creepiest. His behavior towards women was concerning and he didn't treat many people with respect. This all changed when he met Bernadette, however.

RELATED: Which TBBT Character Has The Best-Paid Job?

Howard went from a wannabe womanizer to a loving husband and father of two. At work, Howard's career as an engineer got him to outer space and a job with the United States Military. As outgoing and goofy as Howard was, his contributions to science were some of the most impressive in the group and he was one of the best-paid jobs. It was eye-opening to see someone make a complete transformation in all areas of his life.

Sheldon Cooper Became A Better Scientist And Even Better Man

Sheldon Cooper delivers his Nobel Prize speech in The Big Bang Theory

It shouldn't be too surprising that Sheldon's character arc was the best among his friends. He became a more developed person than the man viewers met in season 1. With the help of his wife Amy and friend Penny, Sheldon was able to understand sarcasm, became a better listener, and became a more thorough scientist. He warmed up to new people and the art of being selfless. All of the changes helped him become a Nobel Prize winner by the finale.

Sheldon dedicated his life to science but grew as a man, partner, and friend at the same time. Sheldon still had annoying tendencies but he was a more understanding man by season 12.

NEXT: The 5 Most Annoying Things Sheldon Ever Did On The Big Bang Theory (& 5 Sweetest)