Dr. Jekyll and Mr. Hyde

The Strange Case of Doctor Jekyll and Mr Hyde is a book by Robert Louis Stevenson, in which Doctor Jekyll, attempting to create a potion which will separate his good and evil sides, instead creates a potion which just allows his evil side--Mr. Hyde--to manifest. Since Mr. Hyde looks different from Dr. Jekyll, he can commit crimes that Jekyll will never be suspected of. The problem? Mr. Hyde commits murder. And then Jekyll discovers he's transforming without the help of the potion.

The novel has been re-imagined many times throughout the years, including a highly popular stage musical and several films of varying quality.