A Pen Name (also known as a pseudonym) is a made-up name a writer or artist (in the case of performers, this is called a Stage Name) produces works under for whatever reason. (Rule of Cool, mostly, or in the case of famous actors / people, it's also a way to find out whether or not they'd be succesful even without their star power attached to it.) Supertrope of Moustache De Plume and Same Face, Different Name, so please don't repeat those examples here.