Josef Issels (1907–1998) killed Bob Marley.
Okay, not really. Cancer killed Bob Marley. But Issels wasn't very helpful. Issels is responsible for developing "Issels Combination Therapy", which is an alternative to standard cancer treatment procedures. The Issels plan is based largely on diet, laetrile, chelation, and the removal of fillings from the patient's teeth. The regimen has been panned by Quackwatch and Cancer Research UK.
When Marley was diagnosed with melanoma, he eschewed medical treatment and instead consulted Issels. He died less than a year later.
British Olympic gold medal winner Lillian Board was another one of Issels' stunning successes. She was diagnosed with colon cancer in 1970 with a life expectancy of about two months left (as the cancer had already spread by this time). She spent the last month-and-a-half of her life having her tonsils and front teeth removed (as they supposedly helped spread the infection) and drinking only spring water and herbal tea. While her death wasn't preventable as Bob Marley's was, one could say that Board's last month-and-a-half were slightly wasted by this quack with painful and unnecessary "treatments".