Over the course of its impressive 12 season run, the hit CBS series The Big Bang Theory introduced viewers everywhere to many unique characters, ranging from physicists to geologists to engineers to Cheesecake Factory waitresses. The series followed the daily life of the main group of nerdy friends, as well as their subsequent romantic relationships and misadventures.

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After its lengthy run, the series finally came to an end in May 2019, but not without first producing a spin-off series, Young Sheldon. But not even that was enough to satisfy the eager Big Bang fans, who are still hoping for more spin-offs to come. Here are some characters who definitely deserve a spin-off - and some who really do not.

Deserve A Spin-Off: Professor Proton

The Big Bang Theory - Bob Newhart as Professor Proton with Sheldon

Professor Proton would arguably be one of the easiest characters to create a spin-off series for, given the fact that the entire Professor Proton character was taken from a television show within the Big Bang universe.

The beloved television scientist was the star of Sheldon and Leonard's childhood favorite series. It would be fun for a version of that show to be produced - something Young Sheldon has even teased on a few occasions with small clips here and there. And if they could find a way to ensure Bob Newhart continued in the role, all the better.

Don't: Leonard

Big Bang Theory Leonard hands Penny a document

At one point in time, Leonard was meant to be the main character of The Big Bang Theory. Just look at some of the series' earliest episodes and it's clear. But thankfully, the show quickly realized the error of its ways, turning into much more of an ensemble series, with a secondary focus on Sheldon and Leonard as a duo.

Leonard was just never interesting enough on his own to hold a storyline, let alone a series all together. Giving him a spin-off in any form would therefore be a mistake - one that the original series already learned from.

Deserve A Spin-Off: Howard

Howard talking on the phone and looking surprised on TBBT

One of the more overlooked and often slighted members of the main group of characters, Howard Wolowitz is a character with a rich personal life - both in the present and the past.

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Given Howard's work in space and aerospace engineering, there's plenty that could be done with his continued work for NASA, should he ever wind up there again. Likewise, Howard has a rich background with a memorable relationship with his mother, and an untapped fractious relationship with his absentee father, which could make for an interesting backstory spin-off.

Don't: Penny

Penny with a glass of wine in The Big Bang Theory

Penny is a great character in many ways. She provides much-needed grounding in some of the guys' adventures and scientific rambling, and thanks to Kaley Cuoco's comedic timing and reactions, she makes for a great comic relief character, too.

But even after 12 seasons, we still know very little about Penny - and very little that warrants her deserving a spin-off of her own. A spin-off could certainly answer some of the many unresolved questions about her character, but it's hard to imagine much interest being there.

Deserve A Spin-Off: Bert

Bert Kibbler smiling to someone off camera on The Big Bang Theory

Sometimes, a supporting character is just so good that you can't get enough of them. No matter how late in the series they join the cast, or how little they are really featured, certain characters just have an innate charm and joy to them that never gets tiring.

Brian Posehn's Bert Kibbler is exactly one of those characters. The incredibly enthusiastic and uber nerdy geologist was never formally added to the main group's circle, but he took part in many of their adventures, including experiments with Amy and the rock band Footprints on the Moon with Raj and Howard.

Don't: Amy

Some supporting characters definitely deserve more screen time. And some series-regular characters definitely deserve a whole lot less. Amy Farrah Fowler is a character that was best used in moderation, before being used in overabundance as the series went on.

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Amy almost always featured in the series to provoke conflict and unneeded change in characters, such as her creepy obsessive feelings of friendship toward Penny, or the way she forced Sheldon to change for her. Over the course of the series, we got to know almost too much about Amy. We don't need more of her.

Deserve A Spin-Off: Wil Wheaton

Wil Wheaton as Wil Wheaton in The Big Bang Theory

More than most other sitcoms, The Big Bang Theory had a truly impressive number of celebrity guest stars, ranging from science fiction icons to famed scientists. Most of the guest stars even appeared as themselves, albeit often over the top and satirized versions of themselves. But none of them made quite the impact that Star Trek veteran Wil Wheaton did.

As Sheldon's on again, off again nemesis, Wheaton had a major recurring role in the series, getting involved with basically everyone's storylines, and eventually became the new Professor Proton. There would be plenty of territory to cover with a series focusing on this over the top Wheaton.

Don't: Kripke

John Ross Bowie as Barry Kripke in The Big Bang Theory

In the world of sitcoms, it's easy for a character to be made entirely out of a simple premise, such as a caricature, a stereotype, or a single defining trait or behavior. It's also true that these characters, while useful for quick jokes or snickers, shouldn't be given more attention than they really need.

It's for that reason that recurring antagonist Barry Kripke was best utilized as a minor character. The majority of his personality and the jokes made at his expense are reliant upon his speech impediment, and that kind of characterization is hardly needed in television these days.

Deserve A Spin-Off: Raj

Raj standing with Howard in the comic book store TBBT

Though Howard may have been pretty overlooked, no character was as underused and unjustly made fun of as Raj was during the entire series' run. One of the funniest characters in the series, as well as completely adorable and a true romantic at heart, Raj underwent one of the biggest transformations over the course of The Big Bang Theory.

But at the end of the series, his story still didn't feel complete. Despite being the biggest romantic of the group, Raj never managed to find his happily ever after. For that reason alone, he deserves a spin-off.

Don't: Priya

Aarti Mann as Priya Koothrappali in The Big Bang Theory

Few characters in the history of The Big Bang Theory truly added as little to the series as Raj's sister, Priya. Primarily introduced in the series for the sake of creating tension between Penny and Leonard, Priya is the Big Bang universe's equivalent of Friends' Emily: a character so grating, it's hard to understand how they were created in the first place.

So while Raj may deserve a spin-off of his own, and perhaps more than any other character in the series at that, there's absolutely no reason a wholly irritating character like Priya should be given one.

NEXT: Big Bang Theory: 5 Reasons Why It Needs A Sequel (& 5 Why It Doesn't)