Kevin Sussman (series regular)
HBO Max
Lauren Lapkus (series regular)
HBO Max
Lauren Lapkus made her “Big Bang Theory” debut as Denise, the Comic Center of Pasadena’s new assistant manager, in Season 11’s “The Comet Polarization.”
After accompanying Stuart to Sheldon and Amy’s wedding, Denise returned the following season as Stuart’s girlfriend. In her final appearance, Season 12’s “The Maternal Conclusion,” she invited Stuart to move in with her.
All told, she appeared in just eight of the sitcom’s 279 episodes.
Lapkus reprises her role — now as a series regular — in “Stuart Fails to Save the Universe.”
Brian Posehn (series regular)
HBO Max
Brian Posehn made his “Big Bang Theory” debut as geology professor Bert Kibbler in Season 6’s “The Contractual Obligation Implementation,” though the character initially went unnamed. Bert was formally introduced in Season 7’s “The Occupation Recalibration” and went on to recur throughout the remainder of the sitcom’s run, appearing in 15 of its 279 episodes.
Posehn reprises her role — now as a series regular — in “Stuart Fails to Save the Universe.”
John Ross Bowie (series regular)
HBO Max
John Ross Bowie made his “Big Bang Theory” debut as fan-favorite physicist Barry Kripke in Season 2’s “The Killer Robot Instability,” immediately establishing the speech-impaired scientist as a thorn in Sheldon Cooper’s side. He went on to appear in 25 episodes across 11 seasons before making his final appearance in Part 1 of the sitcom’s two-part series finale in 2019.
Among the sitcom’s recurring players, only Kevin Sussman appeared in more episodes.
Bowie reprises his role — now as a series regular — in “Stuart Fails to Save the Universe.”
Josh Brener
HBO Max
Josh Brener first appeared on “The Big Bang Theory” in Season 5’s “The Flaming Spittoon Acquisition” as Comic Center employee Dale. He reprised the role in Season 6’s “The Tangible Affection Proof.”
He returns to the franchise in “Stuart Fails to Save the Universe,” this time as an entirely new character: Trevor, one of Stuart’s most frequent customers. He first appears in Episode 1.
Ryan Cartwright
HBO Max
Ryan Cartwright made his first (and only) appearance on “The Big Bang Theory” in Season 6’s “The 43 Peculiarity,” playing Penny’s community college classmate Cole.
He returns to the franchise in “Stuart Fails to Save the Universe,” this time as an entirely new character: Kyle, a daily patron of Stuart’s comic book store. He first appears in Episode 1.
Penn Jillette
HBO Max
Penn Jillette made his “Big Bang Theory” franchise debut in prequel series “Young Sheldon,” appearing opposite his longtime stage partner, Teller.
In the Season 5 finale, “A Clogged Pore, a Little Spanish and the Future,” 12-year-old Sheldon (played by Iain Armitage) struggled to cope with the first signs of puberty. After getting his first pimple, Penn and Teller appeared as Acne Vulgaris and his silent sidekick, Pus.
As first revealed in the trailer for “Stuart Fails to Save the Universe,” Jillette returns to the franchise, this time as himself in Episode 1’s post-apocalyptic wasteland.
Teller
CBS
Magician and illusionist Teller made his “Big Bang Theory” debut in Season 11’s finale, “The Bow Tie Asymmetry,” as Larry Fowler, Amy’s taciturn father. He reprised the role twice during the sitcom’s 12th and final season.
He later reunited with longtime stage partner Penn Jillette in the Season 5 finale of prequel series “Young Sheldon,” playing Pus, the silent half of the dermatological duo Acne and Pus, as 12-year-old Sheldon (Iain Armitage) grappled with his first pimple.
As first revealed in the trailer for “Stuart Fails to Save the Universe,” Teller returns to the franchise, this time as himself in Episode 1’s post-apocalyptic wasteland.
Kunal Nayyar
HBO Max
Raj becomes the first member of the original “Big Bang Theory” ensemble to appear in “Stuart Fails to Save the Universe,” though the version audiences meet is far removed from the astrophysicist we last saw in the CBS finale. Held prisoner for years in Grand Caliph Barry Kripke’s post-apocalyptic Pasadena, this alternate-universe Raj is the only one capable of repairing the quantum interference device that can restore the original timeline.
In a particularly cruel twist, this Raj has finally achieved the happy ending that eluded him in the original series — he even rode an elephant to his wedding — only for his wife to be devoured by a giant moth shortly afterward. Before he can put his scientific expertise to use, Raj is fatally shot by Kripke, becoming the spin-off’s first major casualty in Episode 1.
Christine Baranski
CBS
Christine Baranski earned four Primetime Emmy nominations for her recurring role as Leonard’s acerbic mother, Dr. Beverly Hofstadter, on “The Big Bang Theory.” Introduced in Season 2’s “The Maternal Capacitance,” Beverly appeared in 16 episodes across nine of the sitcom’s 12 seasons.
As revealed in the trailer for “Stuart Fails to Save the Universe,” Baranski returns to the franchise. Whether she’s reprising Beverly, playing an alternate-universe version of the character, or something else entirely remains under wraps.
Riki Lindhome
CBS
Riki Lindhome made her “Big Bang Theory” debut in Season 2’s “The Cooper-Nowitzki Theorem” as Ramona Nowitzki, a graduate student (and later doctor) with an unrequited crush on Dr. Sheldon Cooper (played by Jim Parsons).
Ramona resurfaced in Season 10’s finale, “The Long Distance Dissonance,” making an unwelcome advance that prompted Sheldon to fly across the country and propose to Amy (Mayim Bialik). She returned one last time in the Season 11 premiere, “The Proposal Proposal.”
As revealed in the trailer for “Stuart Fails to Save the Universe,” Lindhome returns to the franchise. Whether she’s reprising Ramona, playing an alternate-universe version of the character, or something else entirely, however, remains under wraps.
Joshua Malina
CBS
Joshua Malina first appeared on “The Big Bang Theory” as the oft-mentioned President Siebert (first name unknown) in Season 4’s “The Benefactor Factor.” He returned for two additional appearances in Season 5 before recurring throughout Seasons 11 and 12, appearing in 13 episodes overall.
As revealed in a teaser trailer for “Stuart Fails to Save the Universe,” Malina returns to the franchise, seemingly as a member of the United States Army. The full extent of his role remains under wraps.
Wil Wheaton
CBS
Wil Wheaton made his “Big Bang Theory” debut in Season 3’s “The Creepy Candy Coating Corollary,” playing a heightened version of himself. Initially established as a frenemy of Dr. Sheldon Cooper, Wheaton eventually became a friend of Sheldon and a frequent presence in the group’s lives, appearing in 17 episodes across nine seasons.
As revealed in an HBO Max sizzle reel, Wheaton resurfaces in “Stuart Fails to Save the Universe.” He appears inside Stuart’s comic book store, seemingly firing an energy blast at Stuart, Denise, Bert, and Kripke, suggesting he’s some sort of wizard — or at least hails from one of the show’s more magical alternate realities.
New episodes of “Stuart Fails to Save the Universe” release Thursdays at 9 p.m. ET on HBO Max.