- Leonard Hofstadter
- Sheldon Cooper
- Howard Wolowitz
- Raj Koothrappali
- Amy Farrah Fowler
- Bernadette Rostenkowski-Wolowitz
- Stuart Bloom
The recurring character with the most appearances on The Big Bang Theory was a character we didn't actually see much of at all: Howard's mother, Debbie Wolowitz, who was voiced by Carol Ann Susi. Following in the tradition of Rhoda's doorman Carlton, Cheers' Vera Peterson and Frasier's Maris Crane, we never properly saw Howard's overbearing Jewish mother. Carol Ann Susi passed away in November 2014 after a short illness. Following her passing, her character Mrs. Wolowitz was said to have died while on vacation in Florida in a February 2015 episode of the show.
John Ross Bowie appeared as Barry Kripke, an annoying colleague of the guys, in twenty-five episodes starting in the second season. Although Sheldon once tried to befriend Barry to secure access to a university computer and later briefly made Barry a part of his replacement social group, neither Sheldon nor Leonard are particularly fond of Barry.
Wil Wheaton appeared as a fictionalised version of himself in seventeen episodes since The Big Bang Theory's third season. Wil started off as a mortal enemy of Sheldon but later become friends with him and the wider group.
Mary Cooper is Sheldon's devoutly Christian mother, played by Laurie Metcalf, who appeared in fourteen episodes of The Big Bang Theory dating back to its first season.
Christine Baranski guest starred as Beverly Hofstadter, Leonard's detached neuro-scientist mother who shares many attributes with Sheldon, in sixteen episodes beginning in the show's second season.
Raj's sister Priya, played by Aarti Mann, was a prominent character in Season 4 of The Big Bang Theory and into the show's fifth season. Priya and Leonard dated during the show's fourth season, but the relation ended in the fifth season when Priya moved back to India. Raj's parents, Dr. and Mrs. Koothrappali, played by Brian George and Alice Amter respectively, appeared in multiple episodes of the show since the first season. Dr. Koothrappali visited Pasadena in December 2014, marking the first time the character had been seen "in person".
Brian Thomas Smith appeared as Zack Johnson, Penny's on-again-off-again ex-boyfriend, in eleven episodes starting with the third season finale.
Brian Posehn made fifteen appearances as Bert Kibbler, a geologist at Caltech, starting in the sixth season.
Dean Norris appeared in six episodes of The Big Bang Theory's tenth and eleventh seasons as Colonel Williams, an Air Force representative who dealt with the guys' quantum gyroscope project.
Regina King guest starred as Janine Davis, the director of human resources at the university, in six episodes of The Big Bang Theory since the sixth season.
Bob Newhart made six appearances as Professor Proton / Arthur Jeffries starting in The Big Bang Theory's sixth season.
Penny's father, Wyatt, played by Keith Carradine, appeared in five episodes since the fourth season of The Big Bang Theory.
Riki Lindhome guest starred in three episodes as Ramona Nowitzki, a grad student with a big crush on Sheldon, going back to the second season.
Judd Hirsch appeared as Alfred Hofstadter, Leonard's father, in two episodes starting in the ninth season.
Kathy Bates guest starred as Amy's mother, Mrs. Fowler, in three episodes beginning in the eleventh season.
This page has been updated to episode 1224. The Stockholm Syndrome