- Leonard Hofstadter
- Sheldon Cooper
- Howard Wolowitz
- Raj Koothrappali
- Amy Farrah Fowler
- Bernadette Rostenkowski-Wolowitz
- Stuart Bloom
The recurring character with the most apperances on The Big Bang Theory is a character we haven't actually seen very much of at all: Carol Ann Susi who provided the voice of Howard's mother, Mrs. Debbie Wolowitz. Following in the tradition of Cheers' Vera Peterson, Frasier's Maris Crane and Rhoda's doorman Carlton, to name just a few unseen TV characters, we have never properly seen Howard's overbearing Jewish mother. Carol Ann Susi passed away in November 2014. Following her passing, her character Mrs. Wolowitz died while on vacation in Florida in a February 2015 episode of the show.
Raj's sister Priya, played by Aarti Mann, has appeared in twelve episodes of The Big Bang Theory. 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, have appeared in the show since the first season. Dr. Koothrappali visited Pasadena in December 2014, marking the first time the character has been seen outside of a computer screen.
John Ross Bowie has appeared as Barry Kripke, an annoying colleague of Leonard and Sheldon at Caltech, in eighteen episodes. Although Sheldon tried to befriend Barry once to access an open science grid computer and briefly made Barry a part of his replacement social group when Leonard & the gang were hanging with Priya, neither Sheldon nor Leonard seem particularly fond of Barry.
Mary Cooper is Sheldon's devoutly Christian mother, played by Laurie Metcalf, who has appeared in nine episodes of The Big Bang Theory dating back to its first season. Beverly Hofstadter, played by Christine Baranski, is Leonard's neuroscientist mother who shares many attributes with the brilliant Sheldon. Christine Baranski has also appeared in nine episodes of the show. Penny's father, Wyatt, played by Keith Carradine, has appeared in two episodes.