Tom Waits is often underrated and never duplicated. He is a tremendous singer-songwriter, composer and actor.
I love this description of his voice.
Waits has a distinctive voice, described by critic Daniel Durchholz as sounding "like it was soaked in a vat of bourbon, left hanging in the smokehouse for a few months, and then taken outside and run over with a car." With this trademark growl, his incorporation of pre-rock music styles such as blues, jazz, and vaudeville, and experimental tendencies verging on industrial music, Waits has built up a distinctive musical persona.
IMHO, Waits is an American treasure.