Thought I'd post this while I have a chance.
Name: Dr. Heather Jekyll/Ms. Evelyn Hyde
Bio: Dr. Jekyll was a scientist who was interested in the human mind. The doctor theorized that within the mind, there was a constant battle of good and evil, and she believed that if she could find a way to separate evil from good, then people would be able to live a life without human-based evils such as murder. She researched for years, and soon concocted a chemical compound. She tested this compound on herself, since she didn't have any willing volunteers, and that created Ms. Hyde.
Normally, when it comes to Jekyll becomes Hyde and vice versa, it could be mistaken for DID, but with this case, there's some slight physical changes. These changes include height, eye color, hairline, and jawline. With the physical changes and the change in personality, Hyde is considered a completely different person than Jekyll.
At first, Jekyll and Hyde needed to drink the concoction in order to switch, but at this point in time, Hyde is strong enough to take control when Jekyll is either angry, feels threatened, or asleep. Eventually, Hyde will become strong enough to take over whenever he pleases.
Hyde is much stronger than Jekyll in terms of physical strength, has a keener sense of smell (keen enough to be able to tell when somebody's lying), and it would turn out in the fairy tale world, Hyde is immune to magic while Jekyll is vulnerable.
Dr. Jekyll cooped herself up in her laboratory in order to find a way to get rid of Hyde, after Hyde had killed somebody. But none of the concoctions she came up with worked, and she constantly worried that Hyde would go after Jekyll's friends.
Jekyll's friends, John Utterson, Dr. Hastie Lanyon, and Mr. Poole (the butler), are suspicious because Dr. Jekyll wrote a will that said that if anything happened to her, everything she owned goes to Ms. Hyde, a completely unlikeable and murderous stranger. Jekyll's friends believed that Hyde was blackmailing Jekyll.
Appearance:
Heather JekyllEvelyn Hyde