He closed a lot of his later shows (early '90s) with "Mack the Knife."
I hadn't imagined that! And I can see why. It was an '80s cover (from the 1984 "L.A. is My Lady" album) of a song that had been recorded literally a hundred times before.
If you hadn't caught him live towards the end (and it was honestly kinda sad, almost like seeing an old Muhammad Ali get beat up), you probably never would have thought of it as one of his "signature" songs. And like I said, it was more out of necessity to give him time to breathe, than it was out of popularity.
Although I personally enjoyed the song (but it can't touch Bobby Darin's iconic 1959 number one version

).