What does Prometheus have to do with Frankenstein?

Prometheus is also the Titan who fought against his fellow Titans on the side of Olympians in the gods' war. However, despite Prometheus's help, Zeus ends up turning on him, for a number of reasons. In the novel, Frankenstein seems to be very much associated with Prometheus, the Titan who creates human beings and gives them the gift of fire so that they can keep warm and cook their food. Victor often speaks of the power of electricity, and it is implied that this may be how he animated his creature, just as Prometheus gives fire to the humans he creates to help them live. The creature, just as often, is associated with Zeus, whose weapon is lightning. The first time Victor sees him (after the day he is created), the creature is revealed by lightning; Victor even first seems to have been turned on to science by witnessing the power of lightning. The struggle between Zeus and Prometheus finds a parallel in the struggle between the creature and Frankenstein.

Prometheus is the figure in Greek mythology who stole fire from the gods and gave it to man. For this, he was chained to a rock, where every day a vulture was sent to gnaw at Prometheus's body.
The Prometheus figure thus represents defiance of the gods and the empowerment of men, though Prometheus himself is punished. In Mary Shelley's tale, Frankenstein does the very thing that was previously accomplished only by God: the creation of a living being. But the story takes place in a contemporaneous setting, so Frankenstein is a modern counterpart to the prototypical mythic figure who, while not "creating life," gave man a gift which enabled him to accomplish things never done before.
Mary Shelley wrote at a time when the Romantic movement was conceptualizing man as a semi-divine figure. The old limits imposed by religion upon man had begun to be rejected during the eighteenth-century Enlightenment, and during the Romantic period which followed, writers and people in the arts generally were committed to this changed view of humanity. The irony of Shelley's story is that man's new power to create backfires against him. It is a moral parable about the weaknesses of human beings in spite of their new ability to advance and create.

The subtitle of Shelley’s Frankenstein is “The Modern Prometheus.” In Greek myth, Prometheus was the Titan who created humankind and then stole fire from Zeus for his creations. Just as Prometheus did, Victor Frankenstein creates life and then must face the responsibilities of a creator. Zeus ends up punishing Prometheus by chaining him to a rock, where an eagle would peck out his liver every day, only for it to regrow and happen again. His punishment was to suffer for eternity, a fate echoed by Victor’s prolonged suffering.