Dr Frankenstein is the real monster has he created a being made out of corpse, as Dr Frankenstein ignored the fact that he had the responsibility of teaching the monster how live life. Doing this the monster became an evil creation, it when he killed Elizabeth and William
Dr Frankenstein had decided to play God and created a man, he didn't think about how he should care and nurture his creation expect leaving it out on its own. Even though the monster left the lab of Dr Frankenstein, Dr Frankenstein didn't accept what he made and regretted it, without trying to care, so the monster had learn everything by himself.
Because the monster was one of a kind he was lonely and sad he didn't have any companion because who ever took one look at the monster was afraid and thought the monster was evil without getting to know him and judged him by his looks.
The monster was a caring and loving person and only Agathe who was blind saw the good side of the monster as she was blind, she didn't see the image of the monster.
The monster was treated badly by people from getting shot at by Felix, Agathe brother and getting chased by dogs, therefore the monster became evil and used his strength and ugly image to scare people because no one would have ever wanted to know talk to him and get to no him, expect Agathe.
By playing God Dr Frankenstein was only thinking about himself and his science and didn't think about what he was creating and didn't take the responsibility to care and nurture him as a son as Dr Frankenstein had created the monster. Dr Frankenstein did a selfish thing making him the real monster.