The Big Bang Theory is one of the biggest sitcoms of all time and has only gotten more popular since the show's conclusion in 2019. The series, following a group of socially awkward scientists and their attractive and worldly neighbor, won the hearts of fans all over the world thanks to its brilliant comedy, lovable and relatable characters, scientific backdrop and pop culture references.

While the main ensemble was one of the reasons for its huge success, Big Bang's side characters were just as prominent in making the series the hit it is. Despite less screen time, they are fan favorites just as much as Sheldon (

Jim Parsons) or Penny ( Kaley Cuoco).

10 Leslie Winkle

Roseanne actress Sara Gilbert portrays Leslie Winkle, who was a prominent supporting character during the show's first two seasons. Leslie, a fellow physicist, also works at Caltech University and briefly dates Leonard ( Johnny Galecki) before he gets together with Penny.

After Leslie reveals she has no emotional feelings for Leonard, her hatred towards Sheldon becomes the key focus, and she also has a fling with Howard ( Simon Helberg

). Opinionated and sarcastic, Leslie was the first female scientist to appear on the show, paving the way for Amy ( Mayim Bialik) and Bernadette ( Melissa Rauch).

9 Mr. & Mrs. Koothrappali

Raj's ( Kunal Nayyer) parents, Dr. V. M. Koothrappali ( Brian George) and Mrs. Koothrappali ( Alice Amter), live in India and subsequently often only appear on a computer screen via video chat. However, it's absolutely hilarious when they do, delivering brilliant quips and one-liners.

The Koothrappalis are "vastly wealthy" (in the words of Sheldon) and have high expectations for their son, wanting him to marry a respectable Indian woman, as well as for their daughter Priya (

Aarti Mann). Although they're rarely helpful to Raj, an appearance from them is always a treat.

8 Beverly Hofstadter

Leonard had quite a difficult and lonely childhood, and it all makes sense when viewers meet his mother, renowned psychologist Dr. Beverly Hofstadter ( Christine Baranski). She never showed her son affection as a child, and practically used him as a lab rat for her research.

Any time Beverly visits is always a nightmare for Leonard, but a joy for the similar Sheldon, him being like the son she never had.

Her cold and analytic interactions with the characters are always uncomfortably amusing, but it's also nice to see her warm up to Penny, and even Leonard, near the end of the show.

7 Mary Cooper

Where Leonard's mother is icy and intimidating, Sheldon's mother ( Laurie Metcalf) is warm and homey, with a completely opposing parenting style. A highly religious woman from Texas, Mary believes her son's scientific gift "comes from Jesus", and while she doesn't quite understand it, she loves and mollycoddles her "Shelly".

Mary and Sheldon's conflicting Christian and scientific views make for a great dynamic between the pair, and her interactions with the rest of the gang when she visits are just as delightful. While she occasionally comes out with some questionable remarks, her heart is in the right place.

6 Zack Johnson

When Penny's on-and-off again boyfriend Zach ( Brian Thomas Smith) is introduced in the season three finale of Big Bang, it's immediately obvious that he's not the brightest bulb in the room.

This is confirmed when he thinks that the guys' laser is going to "blow up the moon".

Despite his lack of intelligence, Zach is actually a pretty great guy overall. He takes an interest in the gang's work and is there when needed, whether it's dressing up as Superman so the gang can win a costume contest, or coming over on Thanksgiving to end his accidental marriage to Penny.

5 Arthur Jeffries

Comedy legend Bob Newhart plays Arthur Jeffries, also known as Professor Proton and Sheldon's childhood hero, first appearing in the show's sixth season.

Despite Sheldon's enthusiasm, the aged and tired Arthur doesn't exactly have the same feelings towards Sheldon.

His strange relationship with Sheldon is one of the highlights of his appearances, as well as Newhart's stuttering and dry comedic delivery. Although Arthur does pass away, one of the show's best decisions was having him occasionally return as a spirit guide (and Jedi Knight) in Sheldon's dreams - even if it wasn't his choice.

4 Barry Kripke

Sheldon has a surprising amount of enemies on the show, and one of them is physicist rival Barry Kripke (

John Ross Bowie). Kripke is always scheming and trying to mock Sheldon wherever he can, and knows exactly how to push his buttons - with often hysterical results.

Despite constantly causing trouble for the gang and Sheldon, Kripke still seems to hang out with them an awful lot - whether it's guest starring on 'Fun With Flags' or even singing at Amy and Sheldon's wedding. Sheldon certainly finds his match in Kripe, and it's always great to see the two go head-to-head.

3 Wil Wheaton

On paper, having an actor play a fictionalized villainous version of themselves does sound like a risk, but Big Bang pulled it off brilliantly by having Star Trek and Stand By Me actor Wil Wheaton introduced on the show as one of Sheldon's mortal enemies.

Wil was a true antagonist in the beginning, getting under Sheldon's skin and even manipulating Leonard and Penny to break up, so his team could win at bowling. However, Wil is redeemed and becomes a close friend to the gang. His Trek connection also perfectly taps into the guys' sci-fi and comic book interests.

2 Debbie Wolowitz

Despite never actually appearing on-screen (except for a blink-and-you'll-miss-it second from behind in an episode in season six), Howard's mother's ( Carol Ann Susi) presence is felt throughout the show just as much as any visible character.

Mrs. Wolowitz's loud and grating voice is frequently heard throughout the series, often when she and Howard are yelling at each other from separate rooms. Despite being overbearing, the series establishes Debbie as a loving motherly figure, who is always generous with Howard's friends.

She loves to feed people, and even helps Stuart ( Kevin Sussman) after the comic book store burns down.

1 Stuart Bloom

Despite only appearing as a recurring character during the show's first few seasons, Stuart had become the unofficial eighth member of the Big Bang gang by the final season. Appearing in a total of eighty-four episodes, Stuart goes through quite the transformation as a character.

When viewers first meet the owner of the comic book store, he asks Penny out and actually seems like a pretty confident and cool guy that the gang envy. As he becomes more involved and his arc develops, Stuart is revealed as quite self-deprecating and as equally socially inept as the guys, if not even more so.

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