How did Mary Shelley present each character in Frankenstein as a hero or a villain?
In writing Frankenstein, Mary Shelley depicted characters as inherently good or inherently evil. All of the members of Victor Frankenstein's family and his friend Henry Clerval are all innately virtuous people, almost good beyond belief. Elizabeth is almost unnaturally good and kind and understanding. It is Victor himself, however, as well as his creation, the "wretch," who embody the moral ambiguity that makes Shelley's novel so compelling. It is the essentially "good" Victor who ignores all admonitions against tampering with nature and brings to life the instrument of his own doom. It is the essentially "evil" monster that sought only love and companionship and that turned murderous only after being repeatedly rejected by those to whom it reached out. In Chapters 11 and 12, the creature describes for Victor its experiences at observing humanity, in both its warmest and most melancholy states, as it surreptitiously watches a poor but close family. The creature's depiction of this important period of its existence reveals a caring, intelligent being capable of love, but that, as with its initial rejection by Victor, is forced to haunt the back-roads and woods a solitary, lonely figure. Repeatedly rejected by mankind, it seeks instead the latter's destruction. Even here, however, Shelley offers both the monster and its creator a way out of their mutual conundrum. All the scientist has to do is build a female companion for the creature and it will disappear forever. That Victor cannot bring himself to do this, and witnesses the murder of his beloved bride as a result, further illuminates the extent to which the author sought to humanize the beast while demonizing the human.
Neither Victor nor his creation is inherently good nor evil. Victor is a fundamentally decent human being who has made catastrophic choices. The creature would have existed peaceably if not rejected by its creator but, alas, turns to murder to avenge its rejections. All of the other characters in Frankenstein are lacking in this sense of moral ambivalence. The two main characters, however, are very complex.