Tom Waits has always been unique, and well aware of his unique voice and vocal style, he has been aggressive in protecting it, beginning with his well-publicized suit against Frito-Lay in 1990. An article in today's New York Times provides an update of his efforts and his rationale for spending so much time suing those who use imitators, including an award a week ago in Spain against Audi. Another is pending in Germany against Opel.
In all these cases, an advertiser has approached Waits to use his voice in an ad. Waits says no, and the agency hires another singer to mimic him, the jist being to fool the public into thinking it was Waits singing. The Opel case may be something of an exception because the imitator is only accused of performing in a "suspiciously Waitsian voice." What baffles me is why, given his well-known position, they keep asking him and using imitators after he says no.
Waits has no problems with people performing in a way that imitates his voice, but he does take umbrage at people using his voice to sell underwear and cigarettes. His regards such uses as a violation of his moral rights, as unscrupulous behavior by evil doppelgangers, and theft of his property. He has been 100% successful so far, as all defendants have been "Down by Law."