Frankenstein by Mary Shelley makes us confront the question of how we define humanity and monstrosity. The obvious monster is Victor's creation, an outwardly hideous creature that commits murder and conforms to most of our traditional concepts of the "other" or the monstrous. Yet the monster himself makes quite intelligent and justified accusations that Victor himself is the real monster or villain of the novel.
First, Victor's own ambition to create life shows a sort of overwhelming arrogance. Even worse, in so far as he is a parent to the monster, he is an horribly irresponsible one, not making the effort to bring up his child well and give it the love and sympathy every child deserves. Just as we would condemn a family that failed to love and care for a disfigured child, so Victor's own lack of compassion for his creation seems inhumane.
Finally, the monster starts out as a tabula rasa, a blank slate capable of being imprinted with good or bad characteristics. It is the failure of Victor in his self-centered pursuit of knowledge to imprint the virtues of compassion and love onto the monster that causes the initial problems in the novel. Victor's own coldness and revulsion transform the creature into a monster that mirrors the inner monstrosity of Victor hidden under the guise of a successful, intelligent and social adept, albeit self-centered and selfish, modern man.