In the book the central character called Frankenstein succeeds in bringing dead tissue back to life. He doesn’t create a Zombie but instead creates something capable of independent thought. Frankenstein wants to create an exceptionally good and talented man but instead creates someone ugly that can’t accept his own ugliness and becomes a monster.
Frankenstein is the name of the central character and the monster is best called, “Frankenstein’s monster” though at one point the monster says, “If I have a name my name is Frankenstein because you are my father.” So you can say there are two characters called Frankenstein in the story.
Mary Shelley saw some creepy things when she was a kid and creepy things happened later too. That could have inspired her to write such a creepy book, many people think of her as the original goth. She was British and married the poet Percy Bysshe Shelly.