Carol Ann Susi -- one of the central characters on "The Big Bang Theory" -- died Tuesday after battling cancer ... according to execs on the hit show.
Susi played Howard Wolowitz's mom who almost NEVER appeared on camera -- but whose voice was heard in just about every episode.
'Big Bang' executive producer Chuck Lorre said ... "The Mrs. Wolowitz character became a bit of mystery throughout the show's eight seasons. What was not a mystery, however, was Carol Ann's immense talent and comedic timing."
