Frankenstein's monster or Frankenstein's creature, often erroneously referred to as simply "Frankenstein", is an English fictional character who first appeared in Mary Shelley's 1818 novel Frankenstein; or, The Modern Prometheus. Shelley's title thus compares the monster's creator, Victor Frankenstein, to the mythological character Prometheus, who fashioned humans out of clay and gave them fire.

In Shelley's Gothic story, Victor Frankenstein builds the creature in his laboratory through an ambiguous method based on a scientific principle he discovered. Shelley describes the monster as 8 feet (240 cm) tall and terribly hideous, but emotional. The monster attempts to fit into human society but is shunned, which leads him to seek revenge against Frankenstein. According to the scholar Joseph Carroll, the monster occupies "a border territory between the characteristics that typically define protagonists and antagonists".