Grigori Rasputin had to be poisoned, shot several times, clubbed and then tossed into a frozen river before he was killed.
When he was found, his autopsy showed that he had died of hypothermia, despite the fact that he was found with a bullet hole in his forehead. Also, despite having consumed enough cyanide to kill several men, the autopsy showed no traces of poison.
Some accounts of his death suggest that his murderers had castrated him as well. A museum in St. Petersburg claims to have Rasputin's 12 inch long penis in a jar on display.
(Sources: 1, 2)