Which legendary musician voiced a character for King of the Hill?

To this day, I can't hear the word "propane" without thinking of one of TV's greatest dads: Hank Hill.

Is it possible that King of the Hill is one of the most underrated TV shows ever — and not just animated, but in general?

Not that we needed any more evidence to prove just how great this show was, but it also managed to bring in a legendary musician to voice a recurring character. Who was it?