The Man with 2 Faces

Edward Mordake (or Edward Mordrake) was reportedly the 19th century heir to an English peerage.
He supposedly had an extra face on the back of his head, which could neither eat nor speak, although it could laugh and cry.

Edward begged doctors to have his "demon head" removed, because, supposedly, it whispered satanist language to him at night, but no doctor would attempt it. He committed suicide at the age of 23.