The alien is a device used in literature to signify elements foreign, ignored, repressed, or marginalized in a given society. The alien can also offer an outside perspective, illuminating the complexities and/or exposing the hypocrisies and irrationalities in a set social norms.
In literature, Shakespeare's Shylock in The Merchant of Venice and Mary Shelley's monster in Frankenstein are classic examples of the alien. Numerous other examples abound in subsequent literature and film.
In American television, the character of Spock on Star Trek presented a celebrated example of the alien.