The most disturbing musician I have come across is Atrax Morgue, which was the main project of Marco Corbelli, an Italian. His entire discography and musical statement was about death, disease and mental illness. His albums sound like a psychiatric patient playing with an analog synthesizer while recordings from horror films and serial killer interrogations play in the background. He's a pioneer of a noise genre called Death Industrial.
In 2007 he hung himself, forever cementing him as the poster child and god of Death Industrial.