Robert Louis Stevenson wrote, Dr. Jekyl and Mr. Hyde
"Stevenson’s man found a trick by which he could change himself into the person of another man, make an actual transformation of himself. He could change, not only his internal thoughts and feelings, but also his external looks and actions. Whenever he wanted to turn himself into Mr. Hyde, he took a drug and the miracle was accomplished. He changed his handwriting. He had a separate bank account for Mr. Hyde--everything in life was separate. When Mr. Hyde, (who went down into sin and constantly wallowed in those depths of iniquity) wanted to get away from being Mr. Hyde, he took the drug and went back to being Dr. Jekyl. When the officers were after him, he had simply to go into the laboratory and swallow a pill, and when they arrived the man they were looking for was not there.
That process went on through the years, but this was the peculiar fact about it: Not only by his will could he change himself into another man, and so on back and forth, but he discovered at last, when it was too late that, every time he transformed himself from the good Dr. Jekyl into the evil Mr. Hyde, then Mr. Hyde became increasingly the stronger, until at last the climax was reached. It became harder and harder to make the transfer, and then, it could not be made at all. Dr. Jekyl was dead, and Mr. Hyde still lived, but he was damned to eternal darkness and death, helpless and hopeless."
(source: elbourne.org/sermons/index.mv?illustration+3614)