The kingpin is the number one pin. If hit correctly with the bowling ball, the kingpin will make all the other nine pins fall. And that is the object of the game.
It kind of encompasses all of my favorite, like Sinatra songs and Bobby Darin songs and kind of just that whole era but this is like my kingpin for that.
Yet the expression can also be used to describe the top person in any area. A kingpin is another word for an important person. The expression comes from the game of bowling.