Longest-running sketch comedy series in US TV history, and one of the most prolific in terms of cast members becoming stars in their own right after appearing on it.
Originally titled NBC's Saturday Night (and still introduced as "Saturday Night" during the opening sketch). This was due to a competing series titled Saturday Night Live with Howard Cosell launching one month earlier. The series was officially retitled Saturday Night Live in March 1977, a year after the Cosell series ended. (Coincidentally, several cast members from the other show, most notably Bill Murray, later joined SNL).
Although plans for an actual Saturday Night Live Movie fell apart, many motion pictures have been spun-off from SNL based upon skits and short films, arguably the most popular of which were The Blues Brothers (1980) and Wayne's World (1992), both of which spawned sequels.
To mark the 40th anniversary of the series, NBC began airing SNL Vintage during the 2014-2015 season, a prime-time series featuring highlights from past seasons of SNL.
Spin-off series: TV Funhouse, a Comedy Central series that aired from 2000-2001 based upon the Saturday TV Funhouse segments of the late 1990s.
@Gemsmfan: Kaufman wasn't a regular but he was on several times and yeah he did Elvis and Mighty Mouse too. One reason he didn't continue with the show was they asked viewers to vote if Kaufman should be allowed to stay on the show, and nearly 200,000 viewers voted to "Dump Andy."
I make no apologies for the huge cast list on this one. I think most will agree this show is a special case since so many cast members went on to stardom, and a few established stars also took part. I did not attempt a complete listing: listed here are the longest-serving cast members and those who I know went on to stardom and/or have other shows listed here. As a result many names are left out, including numerous more recent cast members. Obviously if there is anyone you feel should be included but isn't, please add their names. Edit: added Alec Baldwin and Steve Martin, the two record-holders for most times as guest host (since both have hosted more than 15, more episodes than the complete runs of some shows).