"The Big Bang Theory" found great opportunities to flesh out the main characters by introducing members of their extended families. Arguably the most well-known is the enigmatic mother of Howard, Mrs. Wolowitz, who became a vital piece of the "Big Bang" puzzle, even though she was generally kept hidden from viewers.
When Mrs. Wolowitz first appeared in Season 1, her comically thick New Jersey accent and harsh banter with Howard made her an instant fan-favorite. The actress behind the voice, Carol Ann Susi, died in 2014, so the writers elected to write out Howard's mom entirely, and her final appearance was in Season 11 via archival audio footage.
While Mrs. Wolowitz was mostly portrayed through voice-over; there are two notable exceptions where fans saw her physical form. During Season 5, she appears in an aerial shot of Howard's rooftop wedding. Then, in Season 6, viewers can briefly glimpse her body as she passes in front of a doorway.