Big Bang's Best Recurring Characters

The Big Bang Theory's success is thanks in no small part to its terrific cast — an ensemble that extends well beyond its seven series regulars.

Over 12 seasons and 279 episodes, the CBS sitcom introduced myriad recurring characters that the audience grew to love almost as much as Sheldon, Penny et al. Those include family members (such as Leonard's mom Beverly), fellow Caltech scientists (such as geologist friend Bert) and real-life pop-culture figures (such as Wil Wheaton).

Below, TVLine ranks some of those tertiary characters...

#1. Mrs. Wolowitz

Voiced by: Carol Ann Susi

Total number of appearances: 40

First appearance: "The Dumpling Paradox" (Season 1, Episode 7)

Last appearance: "The Bitcoin Entanglement" (Season 11, Episode 9 – posthumously)

Best moment: In Season 4's "The Cohabitation Formulation," Debbie is startled by the sound of someone entering her home. "Who's there? Are you a sex criminal?" she asks. "Sex criminals don't have KEYS, Ma!" Howard responds. (WATCH)

#5. Arthur Jeffries (aka Professor Proton)

Played by: Bob Newhart

Total number of appearances: 6

First appearance: "The Proton Resurgence" (Season 6, Episode 22)

Last appearance: "The Planetarium Collision" (Season 12, Episode 5)

Best moment: In Season 7's "The Proton Transmogrification," the late Arthur is confused when he visits Sheldon in a dream and is dressed as Obi-Wan Kenobi. ("I'm not familiar with that. Is that... an Internet?" he asks, in Newhart's signature deadpan tone.) (WATCH)

#6. Barry Kripke

Played by: John Ross Bowie

Total number of appearances: 25

First appearance: "The Killer Robot Instability" (Season 2, Episode 12)

Last appearance: "The Change Constant" (Season 12, Episode 23)

Best moment: In Season 5's "The Beta Test Initiation," Kripke tries (and fails) to get Siri to recommend a restaurant — which may or may not have something to do with his speech impediment. (WATCH)

#3. Beverly Hofstadter

Played by: Christine Baranski

Total number of appearances: 16

First appearance: "The Maternal Capacitance" (Season 2, Episode 15)

Last appearance: "The Maternal Conclusion" (Season 12, Episode 22)

Best moment: In the series' antepenultimate episode, Leonard (finally!) confronts his ice queen of a mother, who extends an olive branch in the form of a hug. (WATCH)

#9. Janine Davis

Played by: Regina King

Total number of appearances: 6

First appearance: "The Egg Salad Equivalency" (Season 6, Episode 12)

Last appearance: "The Inspiration Deprivation" (Season 12, Episode 19)

Best moment: In her final appearance, the HR rep shuts her office door and pours two glasses of scotch — one for her, and one for Amy — to celebrate Amy potentially becoming the fourth-ever woman to win a Nobel prize. (WATCH)

#4. Mary Cooper

Played by: Laurie Metcalf

Total number of appearances: 14

First appearance: "The Luminous Fish Effect" (Season 1, Episode 4)

Last appearance: "The Bow Tie Asymmetry" (Season 11, Episode 24)

Best moment: In Season 8's "The Maternal Combustion," Mary and Beverly get into a heated debate about science vs. religion — or, more specifically, the merits of "bearded Jewish guys" Sigmund Freud and Jesus Christ. (WATCH)

#8. Mike Rostenkowski

Played by: Casey Sander

Total number of appearances: 6

First appearance: "The Launch Acceleration" (Season 5, Episode 23)

Last appearance: "The Spock Resonance" (Season 9, Episode 7)

Best moment: In Season 5's penultimate episode, Mr. Rostenkowski encourages Howard to face his fears and follow through on his space mission — even if that means postponing his wedding to Bernadette. (WATCH)

#2. "Wil Wheaton"

Played by: Wil Wheaton

Total number of appearances: 17

First appearance: "The Creepy Candy Coating Corollary" (Season 3, Episode 5)

Last appearance: "The D&D Vortex" (Season 12, Episode 16)

Best moment: In his first episode, Wil competes with Sheldon in a Mystic Warlords of Ka'a competition, and uses the theoretical physicist's love for his Meemaw against him. (WATCH)

#10. Wyatt

Played by: Keith Carradine

Total number of appearances: 5

First appearance: "The Boyfriend Complexity" (Season 4, Episode 9)

Last appearance: "The Donation Oscillation" (Season 12, Episode 15)

Best moment: In his first episode, Penny's dad scolds his daughter for lying to him about her (failed) relationship with Leonard. After she leaves the room, Wyatt pleads with Leonard not to give up on her. (WATCH)

#7. Zack Johnson

Played by: Brian Thomas Smith

Total number of appearances: 11

First appearance: "The Lunar Excitation" (Season 3, Episode 23)

Last appearance: "The Donation Oscillation" (Season 12, Episode 15)

Best moment: In Season 4's "The Justice League Recombination," Zack comes over to "talk science" with the guys. "I saw this great thing on the Discovery Channel... turns out if you kill a starfish, it'll just come back to life," he says. "Was the starfish wearing boxer shorts? Because you might have been watching Nickelodeon," Sheldon replies. (WATCH)