Robert Louis Stevenson 
The Strange Case of Dr. Jekyll and Mr. Hyde 

Dealing with split personalities, Dr. Jekyll battles with himself to overcome the evil Mr. Hyde. An old friend of Dr. Jekyll’s, a lawyer Gabriel John Utterson, investigates odd occurrences that are linked to Mr. Hyde. Dr. Jekyll is determined to stop becoming Mr. Hyde and uses a potion to stop the transition. This works for a time but the need for the potion increases because he can’t stave off the beast.