Don Rickles and Joan Rivers

Don Rickles was a familiar presence (both as guest and guest host) on "The Tonight Show Starring Johnny Carson" from his 1965 debut until 1979.  That year, David Letterman began filling the host chair much of the time Johnny was away.  Rickles had only five appearances that year, three in 1980, and none in 1981 or 1982.  In the late 70s/early 80s, it seemed Johnny (for various reasons) began paring back some of his regulars.  My guesses...

-Joey Bishop and McLean Stevenson were no longer "hot"
-Rodney Dangerfield would be increasingly baked
-Robert Klein began appearing more on "Late Night with David Letterman"
-Charlie Callas allegedly shoved Carson during an appearance (I'm not buying it; he may have become too "Vegas")
-David Steinberg transitioned into directing
-David Brenner and Rich Little seemed to annoy Johnny (read: Johnny's fake laughter) in their few post-1980 appearances
-Jerry Lewis seemed to do the same shtick and usually had nothing to promote
-Plus there was a huge new generation of comedians coming up due to SNL and the comedy club boom.

The only ones who seemed to survive this were Buddy Hackett and Don Rickles, who were limited to about one appearance a year.

Rickles returned to the show in 1983 with one appearance, and after that he was always with Johnny until 1992... with one exception.  Here is a shaky, iPhone-kinescoped appearance from 1984 with guest host Joan Rivers.  I hate to admit it, but Rickles was obviously saving his A-game for Carson.