Throughout the history of The Big Bang Theory, the show had several memorable guest stars and supporting characters. Some of the former stars look completely unrecognizable today.

In the following, we're going to put the spotlight on certain supporting characters. During The Big Bang Theory's final interview with Stephen Colbert, that cast members discussed some of their favorite co-stars. It was obvious, Kunal Nayyar's answer proved to be the most popular among the fans.

Let's take a closer look at what the actor had to say, and which guest stars he praised in particular. We'll also reveal who the other cast members praised, and the unique stories attached to certain guest stars.

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Kunal Nayyar Received A Positive Reaction After Referring To Kevin Sussman And Brian Posehn As Memorable Guest Stars

The entire main cast of The Big Bang Theory was featured on The Late Show with Stephen Colbert. During the interview, the cast was asked about their favorite guest stars throughout the 12 season run. Some of the obvious names were mentioned like Bob Newhart and Stephen Hawking. However, Kunal Nayyar's response with Stephen Colbert proved to be the most popular.

Nayyar revealed, "We have a bunch of guys too like Brian Posehn and Kevin Sussman, they bring so much joy to our show. Obviously they're not the Hawking's of the world. But I always love to give them a shout-out."

The moment received a big ovation from the audience, and fans on YouTube also had plenty of praise.

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Fans wrote in the comments section of the clip, "It was so sweet to hear Kunal mention Bert and Stuart actors. Felt like they were also the “extended family." Another fan writes, "Appreciating kunal nayyar's shout out to Bert and Stuart. He is truly a lovely person by heart."

The most liked comments of the clip followed that theme, appreciating Nayyar's tribute to his fellow cast members.

Johnny Galecki Told Stephen Colbert The Unique Story Of How He Got His Favorite Guest Star To Appear On The Show

Speaking of memorable guest stars, Johnny Galecki told the memorable story of how he got Judd Hirsch to do the show. Galecki revealed in the same interview that he went out of his way and cornered the star in order to get him on the show.

via IMDb

Galecki recalls the experience, "Judd Hirsch was a big deal for me. We ran into him at some function and I ran up to him and I said, 'I'm just a massive fan of 'Taxi' and your role on that, and I kind of tried to base the purpose of my character on the purpose of your character.' And then I said, 'you wanna play my dad? You wanna come on and play my dad?' And I realized he might not have any idea what show I'm talking about, or that I'm an actor, even."

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Johnny wasn't exaggerating with the story either, as Judd Hirsch confirmed the details in a separate interview. "He just sort of cornered me one day. We were at a celebration of Jamie Burrows' 1,000th show, and at that celebration - since he did the pilots of all the shows that we know, he did The Big Bang Theory, believe it or not - and Johnny Galecki just came over to me on the stage when it was all over.. 'Would you like to be my father?"

Galecki's approach ended up working as the guest star made a memorable appearance on the show.

The Big Bang Theory Cast Had Different Opinions On Their Favorite Guest Stars

In terms of favorite guest stars, opinions vary among the Big Bang Theory cast. Mayim Bialik is in agreement with Kunal Nayyar, calling Kevin Sussman among the top supporting acts on the show. The cast picked their favorite guest stars with USA Today.

via CBS

Bilalik reveals, "He's part of our family. I learn a lot from him as an actor. He does a lot with a little and he has an understated way of handling things that otherwise could be too much."

As for Jim Parsons, he had praise for the older cast members on the show, particularly Laurie Metcalf and Christine Baranski, who played the roles of Leonard and Sheldon's mothers.

"I see them as actor's actors. All the years that I watched them (before 'Big Bang'), I would identify with them as performers, as a fellow craftsman in the field. To meet them and realize that was true was overjoying. Working with them was as rewarding and interesting as I always thought it would be."

Without a doubt, the show was blessed with top guest stars and a great supporting cast. However, without the contributions of the main cast, the show would not have been successful and enjoyed its lengthy run of 12 great seasons.