Rasputin was extremely difficult to kill, he was poisoned, shot, beat up, chained up and thrown into a river. His cause of death was drowning.
Nah, this isn’t because he was difficult to kill, but because his executioners were nerds with no experience. They shot him in the wrong spot, the poison was too low a dosage, etc.
The idea that he was just comically difficult to kill increasingly to the confusion of his assassins is much funnier though. (Sorry Rasputin for finding your extremely painful death funny but it was a century ago)