Stuart Fails To Save The Universe Episode 2 Surprises With Another Big Bang Theory Legacy Cast Member — Plus, A Last Name Mystery Solved?

What, you didn't think Raj would be the only original cast member from "The Big Bang Theory" to appear on "Stuart Fails to Save the Universe," did you?

Episode 2 of the HBO Max spin-off welcomes four (!) franchise veterans, beginning with Riki Lindhome's Ramona Nowitzki, now a receptionist at Caltech in an idyllic alternate reality where a repressive AI regime keeps everyone in line via microchips implanted in their brainstems.

Later, after one too many outbursts land Stuart, Bert, and Kripke in a reeducation camp, they are shown an introductory video hosted by theater, film, and television's Christine Baranski, playing herself rather than Leonard's mother Beverly.

Then, two-and-a-half years later, upon their release, the trio is kidnapped by the resistance, led by none other than Kaley Cuoco's Penny! Alongside her loyal (if still dimwitted) lieutenant Zack, played by Brian Thomas Smith, Penny attempts to deprogram Stuart, Bert, and Kripke with a series of slaps to the face, believing they hold the key to defeating the AI once and for all.

In reality, however, all they possess is the quantum interference device built by Leonard, Sheldon, and Howard, which allows the group to escape this universe — Denise's AI counterpart in tow after Stuart rescues her from a loveless marriage to Gary.

Their next stop? A universe where magic is real, scientists are burned at the stake, and Bert finds himself moments away from a fiery execution.

Though Kaley Cuoco's Penny doesn't meet the same ghastly fate as Kunal Nayyar's post-apocalyptic Raj in Episode 1, one can safely presume that she — like Zack — was eventually struck down by the AI regime. But because this isn't our Penny from the 12-season run of "The Big Bang Theory," we were more interested in asking the powers that be why she, specifically, was chosen to lead the resistance. Was it simply because she's the last person you'd expect to wage war against the machines?

"You got it," Chuck Lorre tells TVLine in the video interview above. "The fun of this series is the unlikely character assuming a new role."

That said, fellow co-creator Bill Prady argued that Penny is perhaps the character best suited to lead a guerrilla army.

"Penny was always the most capable member of the original group," he says. "If you had to actually get something done, you were probably better off if Penny was in charge of it."

Adds Lorre: "There was always that Nebraska, get-the-job-done quality to her."

But what about lovable dolt Zack? What's his deal — and who would make him second-in-command of a resistance? Prady admits, "That Zack comes along as her lieutenant just made us laugh."

Colin Remas Brown/HBO Max

While Penny's promotion to resistance leader represented a major departure for the character, getting Cuoco back on set felt remarkably familiar for her former co-stars.

John Ross Bowie, for one, found himself right at home in Kripke's familiar dynamic with Penny. Asked whether he was surprised by just how much Barry seemed to enjoy getting slapped around by Penny, the actor laughs: "I do lean into the perv in every episode. But there is that moment where it was kind of fun because Kaley comes over, she smacks me, and they were like, 'Okay, do three in a row.' She hits me three times, and we just started laughing because I was pretending to enjoy it more and more. And she was like, 'Aw, it's just like old times. Look at Barry being inappropriate with Penny.'"

"I have been inappropriate with that actress since 2009," Bowie points out, referring to his Season 2 introduction on "Big Bang." "We have a legacy together of me being inappropriate with Kaley, and so I was not at all surprised [to see Kripke enjoy getting slapped by Penny]."

Kevin Sussman, meanwhile, admits that getting slapped by Cuoco wasn't exactly a hardship. "I mean, I'm not going to lie: Getting slapped around by Penny was quite, quite fun," he says, before Lauren Lapkus interjects: "It was probably one of Stuart's dreams! But I love that scene. Kaley is so badass, and it was so fun to work with her again."

Christine Baranski earned four Primetime Emmy nominations for her recurring role as Leonard's acerbic mother, Dr. Beverly Hofstadter, who appeared in 16 episodes of "The Big Bang Theory" across nine of the sitcom's 12 seasons.

The moment Baranski appears onscreen in "Stuart Fails to Save the Universe" Episode 2, longtime fans are likely expecting the return of Leonard's mom. Instead, the Emmy winner plays herself, starring in propaganda films used to indoctrinate prisoners at the AI regime's reeducation camp. She also gets quite the monologue, warning Stuart et al. that their reeducation will hurt "like a motherf–ker." (But hey, at least they get to live in a world free of anger, war, and insult comics... right?)

For Lorre, however, the biggest thrill wasn't writing Baranski's speech — it was getting to work with her again.

"That was a blast," he says. "She's great. Any chance you get to work with Christine Baranski, even if she helps you do your taxes, do it... But it was one of the great gifts working with her way back when, before I got fired on 'Sybil,' and then as Leonard's mother. She was just extraordinary."

One of Episode 2's blink-and-you'll-miss-it Easter eggs finally— err, maybe — answers a question that "The Big Bang Theory" never did: What is Denise's last name?

Like Penny, whose maiden name was never revealed despite a long-debunked internet theory suggesting it was Teller, Denise — who appeared in just eight episodes of the hit CBS comedy — likewise went without a surname.

In fact, when TVLine visited the set of "Stuart Fails to Save the Universe" in December, the props trailer contained four storage bins labeled Stuart Bloom, Bert Kibbler, Barry Kripke... and simply Denise. At the time, that prompted us to ask Lorre and Prady whether they'd purposely avoided giving Lapkus' character a last name, much as they famously did with Penny.

Lorre, for one, recalled that "along the way, in the 12 years of 'The Big Bang Theory,' we never gave Penny a last name. And at a certain point, we became superstitious about it and thought, 'If you give her a last name, will something bad happen?' So we never did. But I think the same thing happened with Denise."

Prady, on the other hand, argued that Denise "just hasn't needed one yet. She'll get one. Penny never had one, and then ultimately it became a silly thing that we held onto, but I don't think there's a reason to not give Denise a last name." He added, "You have to be careful when you give people last names because you have to think about what it says about them. You have to think about it carefully. So, she'll get one."

That brings us to Episode 2, when Stuart approaches Gary and Denise's apartment and the name Denise Jeffries appears on the intercom system.

"Because it's her married name in that universe," Prady tells TVLine. But if that's the case, why wouldn't Gary's name also be on the intercom?

"Don't bring that up," Penn deadpans.

Prady, meanwhile, offers an explanation worthy of the multiverse: "It really was an issue with the building manager... they got the lease in her name. He had a credit problem." (In other words, don't expect that last name to stick beyond this particular universe.)

For more behind-the-scenes insights from "Stuart Fails to Save the Universe," watch TVLine's full Episode 2 breakdown with the cast and executive producers.