I know this thread is dedicated to female immortal ideas, but on the mention of the Romanav's, i have to mention Rasputin. He is said to have been nearly impossible to kill him. He survived a knife stab, cyanide poisoning, a shot in the back with a revolver, more shots, clubbed, and then was drowned. They burried his body. Men later redug his body and burned it. While he was burning, it is said that the men saw him sit up and attempt to escape the fire.
Like i said, i know this is a guy, but it was too good not to post.