The subject of the alter ego was explored by the famous author Robert Louis Stevenson in his book entitled the Strange Case of Dr Jekyll and Mr Hyde. In the book Dr. Jekyll was the good, restrained upright doctor whereas Mr. Hyde was the evil, unrestrained other self who eventually becomes capable of overpowering the original self.
The fascinating subject has been transferred to the movie screen in famous horror movies starring actors such as Spencer Tracy, Boris Karloff and Michael Caine. The comic side of the alter ego was explored by the comedian Jerry Lewis in the Nutty Professor.
The popular Latin phrase "Alter ego" is now so familiar that it has become part of our own, English language.