It has almost been half a decade since the the finale of the globally acclaimed sitcom The Big Bang Theory. No doubt, the hit sitcom was one hell of a ride, with an impressive cast of characters and character arcs. In fact, the franchise became so famous and loved among the fandom that a spin-off prequel titled Young Sheldon was introduced to give the audience more of Sheldon and his wits.

Indeed, Young Sheldon is still in running with the seventh season on its way. Further, per Variety, there will another addition to The Big Bang Theory universe, though details about the new spinoff show are scarce.

But before the show and its cast exploded into uncharted realms of limelight, many of the familiar faces from the sitcom wanted to be cast as a different character. Of course, it didn't pan out, but for the sake of keeping up with the show, here is the list of actors almost cast in The Big Bang Theory.

Johnny Galecki as Sheldon

Yes, Johnny Galecki was in The Big Bang Theory as Leonard, but it may come as a surprise to many fans of the show that he initially auditioned for the role of Sheldon.

Gradually, after concluding his research for Sheldon, the actor felt more connected to Leonard, and, naturally, the role was passed on to Jim Parson.

In a 2015 interview with Variety, Galecki revealed the reason for declining the role. He said, "I've often been cast as the best friend or the gay assistant of whatever character got to explore those relationships. I said I'd rather play this guy, who seems to have a future of romantic triumphs and difficulties." Truly, when the audience looks back, Galecki was the right choice for the role.

Brie Larson as Penny

While fans can't imagine Penny without Kaley Cuoco, a fabled name that was up for the same role was Brie Larson. Yes, the actor who plays the fan-favorite Captain Marvel in the MCU. In a YouTube video, Larson revealed the details about her audition, however, she never mentioned the role she auditioned for. But since the actor was rejected for being younger than the needed age for playing the character, it is widely assumed she was almost cast to play Penny. Of course, it would have been fun to watch the spin Larson would have brought to the character of Penny, but fans would largely agree Cuoco nailed the role.

Macaulay Culkin as Leonard

Macaulay Culkin is an excellent actor, and it would have been a treat to watch him lending his skills to The Big Bang Theory, if only he had agreed to play the role of Leonard. Well, surprisingly, Culkin was offered the role multiple times, but the actor was not quite impressed with the pitch. And hence Culkin didn't pursue the part. Ultimately, the role went to Galecki, and, truly, Big Bang Theory fans cannot imagine anybody else playing the role.

Kevin Sussman as Howard

Kevin Sussman was inevitably cast in The Big Bang Theory, too, but he played the ever-lost and insecure supporting character of Stuart, whom fans could recall eventually turned into a core character. Before landing the role of Stuart, Sussman was destined to be cast as Howard. But fans know Simon Helberg ultimately ended up playing the character. Next, Sussman even auditioned for the role of Sheldon. Unfortunately, that didn't pan out either. But after that many years, it's really impossible for fans to imagine anyone except Jim Parsons playing Sheldon and Helberg playing Howard — and Sussman playing Stuart.

John Ross as Leonard

John Ross was cast as the ever-hilarious Sheldon's nemesis Barry Kripke. Yes, he was a memorable character who made us laugh with his personality, but Ross was initially interested in the character of Leonard. Obviously, he auditioned for the role — not just once but twice — though sadly, he couldn't make it. But Ross' charm was magnetic enough to land him another significant role in The Big Bang Theory, Barry. Honestly, we would have to be loved to see what new depth Ross would have brought to the character, but he is irreplaceable as Barry.

Kate Micucci as Amy

Amy significantly impacted the arc of The Big Bang Theory the moment she entered. But just like any other role, there were many names up for the character of Amy before Mayim Bialik was finalized. One of the recognizable names was Kate Micucci. Does it ring any bell? Micucci briefly played the role of Raj's love interest, Lucy. Yes, Micucci auditioned for the character of Amy, unfortunately as everyone knows that didn't work in her favor. But without a doubt, her performance as Amy in the audition was indeed remarkable, hence why they offered a different gig.

Amanda Walsh as Penny

It is truly impossible for any The Big Bang Theory fan to imagine the character of Penny apart from Cuoco. But it may come as a surprise to many that before the sitcom premiered and became what we know it today, an entirely different, though unsuccessful pilot of the same show, was filmed. In that version, Amanda Walsh played a character quite similar to Penny, who was supposed to be darker and more humorous than the Penny we know. Fortunately, the show was retooled and a set of new characters were introduced — and by extension Cuoco's Penny, too.

Pamela Adlon as Debbie Wolowitz

Debbie was another interesting character addition to The Big Bang Thory. But sadly she had to be killed off following the tragic demise of Carol Ann Susi, the actor who voiced the role. Before the producers decided to kill Debbie on the show, briefly, they mulled over the possibility of offering the role of Pamela Adlon. However, fans know what exactly when down in the show: Adlon was added to the cast of The Big Bang Theory as she voiced the role of Howard and Bernadette's child Hailey.