It was a fateful summer in 1816 when a highly distinguished group rented the Villa Diodati near Lake Geneva in Switzerland. Along with the eminent poet Percy Bysshe Shelley was Mary Wollstonecraft Godwin (who was already calling herself "Mrs. Shelley" despite his first wife still being alive), their son, and their friend, Clare Claremont. Later joined by poet Lord Byron and his personal physician, John Polidori, what they had all hoped would be a pleasant stay was marked by miserable weather which kept them all housebound for days at a time. Since 1816 was also The Year Without a Summer with abnormal weather patterns disrupting agriculture around the world (and probably caused by the Mount Tambora eruption of 1815), the mood at the villa was not exactly genial.
It's probably not surprising that they amused themselves by sitting around the log fire and reading aloud from a popular anthology of horror fiction. They also spoke at length of new scientific developments relating to the use of electricity in returning dead matter to life (electricity in medicine was all the rage at the time). Whatever the inspiration, Lord Byron then issued his now-famous challenge that each one present would try writing a story with a supernatural theme. While the stories written by Percy Shelley and Lord Byron are not as well known as their other works, John Polidori wrote The Vampyre, the first English vampire novel and, arguably, the beginning of the romantic vampire literary genre (so you can blame him for the Twilight and True Blood franchises).
The most famous of the stories that came out of that summer was by Mary Shelley. Originally only intending to write a short story, she was persuaded by her husband to write a full-length novel instead. Published anonymously in 1818 under the title, Frankenstein: A Modern Prometheus, it was the first true science fiction novel (though modern literary critics tend to dispute that label). As a strange tale of science gone wrong, the novel was not well received by literary critics who viewed it as a "tissue of horrible and disgusting absurdity". The fact that the author was the daughter of a prominent and controversial author as well as a "fallen woman" living in a scandalous relationship raised critical hackles as well. Despite the criticism, Mary Shelley's novel was an immediate success with numerous reprintings, foreign translations, and theatrical productions. The popularity of Shelley's novel, with its various retellings, remakes, movies, etc has ensured her immortality (and definitely made her more famous than her eminent husband) and Mary Shelley's work continues to studied for its literary and feminist content.
As for the actual inspiration for Mary Shelley's work, she would later attribute it to the classical story of Prometheus (hence the novel's title) as well as a "waking dream" (more clinically known as a hypnopompic state) that she had experienced. In describing her dream, she would say that: "I saw the pale student of unhallowed arts kneeling beside the thing he had put together. I saw the hideous phantasm of a man stretched out, and then, on the working of some powerful engine, show signs of life, and stir with an uneasy, half vital motion. Frightful must it be; for SUPREMELY frightful would be the effect of any human endeavour to mock the stupendous mechanism of the Creator of the world."
But were there other sources of inspiration for her novel? As I've already mentioned, the early 19th century was a time of fervent speculation about electricity and its possible medical applications. The potential for using the still-mysterious phenomenon to reanimate dead tissue hardly seemed so implausible and, in fact, several scientists of the time were already making extravagant claims of accomplishing just that (including Giovanni Aldini's electricity experiment on the body of a murderer in 1803). Did Mary Shelley base Victor Frankenstein on one of them? Granted, her novel never directly mentioned electrical stimulation and she never named any one scientist in particular, but there are still several possible candidates for the dubious honour:
Erasmus Darwin While more famous for being the grandfather of Charles Darwin, Erasmus Darwin was legendary in his own right for his extensive scientific achievements. Trained as a medical doctor, he wrote extensively about biology, physics, astronomy, and the origins of life (he formulated one of the first true theories of evolution, in fact). Despite being recognized as one of the finest medical doctors in England (and an early pioneer in the humane treatment of mental illness), Darwin's views on radical politics (he supported the French and American revolutions), his atheism, and tendency to advocate seemingly outrageous ideas (such as humans evolving from lower animals) made him increasingly unpopular in his old age. Although Darwin died in 1802, his being a long-time associate of Benjamin Franklinm as well as a staunch friend of both Lord Byron and Percy Shelley put him in a good position to keep them informed about new developments in the medical applications of electricity. Darwin's lectures on the subject certainly influenced Mary Shelley. In her later memoirs, she would describe listening to Byron and Shelley discussing one of Darwin's experiments in which he preserved the fragment of a worm in a glass case and the possibility of using "galvanism" to reanimate dead tissue (she originally planned to call her novel "Franklinstein" after Benjamin Franklin).
James Lind A second possible candidate was Percy Shelley's old science teacher, Dr. James Lind. Meeting at Eton College during Shelley's last two years there, Lind was an accomplished scientist and medical doctor (men of science tended to be versatile in those days). Despite his reputation as an eccentric, Lind was keenly interested in just about every branch of science and his Windsor residence was packed with various scientific devices including telescopes, Galvanic batteries, and other odd items that made him seem more like an alchemist than a scientist. Along with other scientists of the time, Lind followed Luigi Galvani's research closely and replicated Galvani's use of electricity to stimulate dead frog legs. According to Mary Shelley's unpublished biography of her husband, he and Lind had been extremely close and Shelley regarded him as a second father. While not as famous as other scientists of the time, Lind was a scientific advisor to George III (and even suggested the possible use of electric shocks to treat his mental illness). It was largely as a tribute to Lind that Percy Shelley maintained a lifelong interest in science and medicine and even based one of his own literary characters on the scientist.
Christian Gottlieb Kratzenstein The third candidate (and the only scientist who had not been personally known by either Shelley) was German physican and physicist Christian Gottlieb Kratzenstein. Born in Saxony (now part of Germany) in 1723, Kratzenstein became a professor of physics at Halle University when he was only 23 years old and later became a professor of medicine as well. While he was one of the first scientists to use electricity to treat paralysis, his scientific interests ranged from acoustics to mechanics and he published numerous papers in Danish, French, German, and Latin. He also lived briefly in London and formed numerous contacts with his scientific colleagues in England (including Erasmus Darwin and James Lind, most likely). After returning to Denmark, Kratzenstein continued with his research into treating paralysis with electricity (he also induced "electrosleep" in human subjects) and his scientific papers almost certainly influenced Byron and Shelley. He died in 1795 after a fire destroyed his laboratory.
Johann Conrad Dippel A final dark horse candidate whose name has been frequently suggested as a possible Frankenstein inspiration was the 18th century alchemist and physician, Johann Conrad Dippel. There is no real evidence that Mary Shelley was ever aware of his alchemical research or his quest for an "elixir of life". The only reason that Dippel's name has even been associated with her work is the fact that he was born at Castle Frankenstein near the German town of Darmstadt. And, yes, there is a Castle Frankenstein and Mary Shelley did once travel to Darmstadt although there is no indication that she was even aware of its existence.
Whether Mary Shelley based her novel on any of these scientists, the character of Victor Frankenstein has permanently shaped attitudes concerning the ethical consequences of science as well as creating the stereotype of the mad scientist. The "Frankenstein" label is inevitably invoked whenever a potentially risky new scientific development is discussed in the popular media (regardless of how unlikely the scenario involved may be) and Frankenstein has become a universal cultural icon recognized virtually everywhere (even if people do keep confusing the scientist with his creation). That her novel is so vividly remembered centuries after the author's death may be the best possible tribute for a woman resigned to living in her brilliant husband's shadow.