After almost 50 years as an interviewer, comedian and talk show host, David Letterman’s pedigree on stage feels so firmly established that it’s hard to imagine a situation where he’d be intimidated. But the first time that he performed during open mic night at The Comedy Store back in May of 1975, the Indianapolis native admits that he was deeply afraid to squander what he saw as an opportunity to break into the entertainment industry’s major leagues. “It was like being at the ophthalmologist,” Letterman tells Variety about his debut in the Store’s Original Room.

Mitzi Shore, who passed in 2018 at age 87, had established herself as the Hollywood tastemaker to impress when won the Store from her ex-husband Sammy a year earlier than Letterman’s debut. But within months of its 1972 opening, the storied institution had already begun cultivating its reputation as a pathway to advance comedy careers thanks to Johnny Carson’s regular recruitment of stand-ups from its ranks after moving “The Tonight Show” from New York to Los Angeles at approximately the same time.

Letterman actually never made it on stage the first time that he signed up for the Store’s open mic night (“Regular comics kept showing up and bumping us beginners, so they never got around to the Ls.”) But even if watching more seasoned comedians gave him the opportunity to enjoy the experience of performing without getting hurt himself, he says that being in the spotlight felt no less harsh the following week when he finally got up there. “My first vision of it was this white light,” he remembers. “And that’s all I could see, like I’m having my retina check now on stage. And I did my silly little jokes for five minutes and got off.”

Letterman can’t recall the audience’s reaction (“Applause, no applause, I don’t know”). But he says he remembers the response that was most important to him: “Mitzi said to me, ‘oh, you should come back again’,” he says, affectionately impersonating her flat, Midwestern accent. “I got back in my car and sort of floated up Crescent and to Laurel Canyon and down into north Hollywood where I lived. And from that moment on, it really was the most fun I ever had.”

Byron Allen was just 14 when he first debuted on stage in the summer of 1975, after “Welcome Back Kotter” star Gabe Kaplan recommended that he seek out the Store while making an appearance on a variety show on the NBC lot where his mother was a tour guide. “I thought it was a supermarket where you go to buy jokes,” Allen says. After sitting on the front curb from nine in the morning to 7:30 PM when the building opened, Mitzi originally told Allen that she couldn’t let him in because she’d lose her liquor license.

“She told me to stay in the back parking lot and somebody would come get me, and she gave me two drink tickets and told me ‘don’t go near the alcohol’,” Allen recalls. “Somebody came and I went on stage Monday night in the Original Room, and I think there were four people and 200 chairs. But it was exhilarating — I just knew I wanted to be a comic, and this was the first step to start performing in front of an audience.”

One-man Comedy Store archive Argus Hamilton first took the stage on March 8, 1976, a night which he remembers also marked the debuts of Marsha Warfield and Michael Keaton. Hamilton recalls the date with such specificity because the evening was immortalized in print. “A writer for a supplement in all the Sunday newspapers called Orbit Magazine happened to be in the room that night, and I got a good laugh on my opening joke,” he says. “Orbit was doing a piece on amateur night at the comedy store. They quoted me, and all of my fraternity brothers back in Oklahoma thought I had made it the big time.”

Though he was convinced at the time he’d achieved his “Freddie Prinze moment” of being catapulted overnight into stardom, Hamilton would make three more decidedly less well-publicized pot luck appearances before one of Mitzi’s regulars, Ollie Joe Prater, nominated him for emcee and host at the Store’s Westwood location. That said, he did follow in Prinze’s footsteps and appeared on “The Tonight Show” in 1980. “It was one of the best feelings I ever had in my life,” Hamilton remembers. “I had no idea it was never going to get any better than that, but it was a good feeling.”

By the time Howie Mandel first appeared on the Comedy Store stage, he was already a seasoned performer in his native Toronto. “It was incredibly intimidating,” Mandel admits. “I went up because I had met [Store regular] Mike Binder in Toronto at a club that I was playing there, so he got me in. I was more nervous playing in front of Mitzi than any other audience.” He says that even with an established career, the Store felt like the doorway through which journeymen became name brands—and Shore was the person who decided whether or not to unlock it.

“The key was not going on at the comedy store, but having Mitzi sanction you a regular,” Mandel observes. “Anybody who became a regular had an opportunity to make a living in this business, and without access to the Comedy Store stage, you didn’t have access to Hollywood.”

Like Mandel — albeit a few generations later and using much different material — Iliza Shlesinger was also working steadily by the time she stepped on stage at the Store. Removed by decades from the days when the venue was the first, last and best way for a stand-up to earn time on a national platform like “The Tonight Show” or its many counterparts, it actually took Shlesinger a little while to develop an appreciation for its history and significance. “I didn’t know about the legacy of it,” she says. “It was the longer that I stayed that you start to really get a feeling of reverence for it.”

More than 30 years passed between the Store’s opening and the time Shlesinger became a regular, over which time many aspects of the business changed, including Shore relinquishing the job of booking talent due to her age and advancing health issues. But even if Shlesinger met Mitzi only once, briefly and in passing, she maintains the same affection and respect as the performers before her for the space that the Comedy Store has provided over now five decades to bring stand-up careers to the next level — no matter how brutal it can feel while you’re alone in its spotlight.

“It was always like, why does this place make me anxious? And the answer is, well, because it’s where comics go to die on stage,” she says. “That room is definitely there to humble you. There’s a weight to it that I think a lot of other clubs just don’t have, and you can get smushed under it and never come back or you can use that weight as pressure to make a diamond.”