Who kills William Frankenstein?

The monster, Victor Frankenstein’s creation, kills William Frankenstein. The monster strangles William after meeting him near Geneva. At first, the monster hopes the child might be young enough to accept him without fear or prejudice, but William reacts in terror and says that his father is a Frankenstein. Enraged by the name and by yet another rejection, the monster strangles him to death.

Victor realizes the truth almost immediately when he sees the creature near the site of the murder during a storm. He understands that he himself is actually responsible for William’s death, since he is the one who created the monster. Even though Victor knows the monster killed William, he stays silent because he fears people will think he is insane. That silence leads to another tragedy when Justine Moritz is falsely accused and executed for the crime.

William’s death marks the point where the monster’s loneliness and desire for revenge turn violent. It also begins Victor’s long cycle of guilt and isolation, since he knows the murder is tied directly to his own ambition and failure as the monster’s creator.