Given that the lead characters on "The Big Bang Theory" are all in their twenties and the show gets a lot of laughs out of their occasional (or frequent) immaturity, it's not surprising that their mothers figure prominently in the show, but some more than others.
Beverly Hofstadter, the mother of lead character Leonard (Johnny Galecki) has only appeared a handful of times, but all of those times she actually appeared on screen.
It's Howard's overbearing and patronizing mother who's never seen on screen, though her voice (shouted from another room) has been heard in more episodes -- due to the fact that Howard still lives with her.
The voice doing all the shouting is that of longtime supporting player Carol Ann Susi, whose first screen role came way back in 1974 on the cult thriller series "Kolchack: The Night Stalker." She played an inept news intern in a few episodes.
She's worked steadily ever since, though always in small roles you might or might not remember. Most recently, she played Adam Sandler's mom in his latest comedy feature, "Just Go With It" (2011).
Indeed, it seems she's being typecast in the mom role these days, but at least she's doing it in an incredibly wide variety of films. Prior to Sandler's light relationship comedy, she played a mom in the 2008 slasher film "Red Velvet" and in a 2001 episode of the modern-classic HBO dramedy "Six Feet Under."
Other notable screen turns were as Mrs. Clamato in the mob-film spoof "Jane Austen's Mafia" (1998) and as an admin assistant in the 1987 office comedy "The Secret of My Success." But, faceless though it is, Howard's mom on "The Big Bang Theory" is by far her most famous role.
If you were in fact referring to Leonard's mom, she's played by the more visible Christine Baranski. The award-winning Broadway star first came to the attention of TV audiences as Cybill Shepherd's boozy best friend Maryanne on the popular late-'90s sitcom "Cybill." The series was one of the earliest sitcom creations of Chuck Lorre, who is the real brain behind "The Big Bang Theory."

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