Every Big Bang Theory cameo in Stuart Fails to Save the Universe, so far

In Episode 1, ‘Spoiler: Bert Dies,’ Stuart and the gang stumble upon a post-apocalyptic magic show led by illusionists Penn & Teller while searching for a device to save the universe. It’s a fun blink-and-you’ll-miss-it cameo with an extra treat for longtime The Big Bang Theory fans. Teller, who famously never speaks during performances, previously played Amy’s magic-loving father, Larry Fowler, on TBBT. This also marks his third different role across the franchise, after appearing as the dermatological entity Pus in Young Sheldon.

Episode 1 delivers its biggest surprise with the return of Kunal Nayyar as Raj Koothrappali. He’s one of the original Big Bang Theory gang. But this isn’t the Raj fans remember. He appears as a rugged alternate-universe version, complete with long hair and a beard, and is being held prisoner under Barry Kripke’s rule. Raj manages to crack the complicated math needed to fix the multiverse-breaking quantum device, only for Kripke to shoot him moments before he can reveal the solution. It’s a sad end for Raj, though only in this alternate reality.

Episode 2, ‘Spoiler: Zack’s in This One,’ drops Stuart and his friends into a dystopian alternate universe ruled by an authoritarian AI. Everyone is controlled through electronic devices implanted in their necks that shock them whenever they show “anti-social” behavior. After the trio breaks the rules, they’re arrested and forced to watch a re-education video for rebellious citizens. The surprise narrator and spokesperson is Christine Baranski, who plays herself. Longtime The Big Bang Theory fans will remember her as Dr. Beverly Hofstadter, Leonard’s mother, a role she played from 2009 to 2019.

Episode 2 also brings back Riki Lindhome, reprising her role as Ramona Nowitzki. In this alternate AI-controlled reality, she appears as a Caltech receptionist, where everyone is kept in line by microchips implanted in their brainstems. It’s an interesting twist on her original character from The Big Bang Theory. For those who need a refresher, Ramona was the physics graduate student whose over-the-top obsession with Sheldon Cooper made her one of the sitcom’s most memorable recurring characters.

And we also get to know why Episode 2 is titled ‘Spoiler: Zack’s in This One’. The spinoff brings back Brian Thomas Smith’s endearing goofball, Zack Johnson, in a surprising new way. Just when Stuart, Bert, and Barry think the worst is behind them after 30 months in the AI’s re-education program, Zack shows up and kidnaps them. In the original sitcom, Zack was Penny’s lovable but not-so-bright ex-boyfriend. The pair famously discovered they had unknowingly remained married for years after a drunken Las Vegas wedding.

Episode 2 doesn't make fans wait long for another big return as Kaley Cuoco reprises her role as Penny. In this alternate reality, Penny is leading the resistance against the AI overlord. Zack is working for her and carries out her orders to kidnap the trio. Believing Stuart, Bert, and Barry hold the secret to defeating the AI, she repeatedly slaps Stuart in an effort to deprogram him. When AI drones storm their hideout, the group is forced to flee and continue their multiverse adventure. In the Big Bang Theory, Penny was the warm-hearted neighbor who eventually married Leonard Hofstadter.