Mary Shelley's Frankenstein is not only my favorite horror novel; it's one of my favorite novels, period. It has become part of Western culture to the point that the very title is now synonymous with science gone wrong and tampering with the rules of life and death.
Just as fascinating as the novel itself are the circumstances under which it was written. As a kid, I was amazed that this horrible monster had been dreamed up by a teenage girl (some magazine - it might have been Dynamite - told this story with a breathless "she was a kid JUST LIKE YOU!" sense of wonder).
Mary Shelley was a real-life Margo Tenenbaum: daughter of two famous philosophers (her mother, Mary Wollstonecraft, was a pioneering feminist; her father, William Godwin, a forerunner of modern anarchism), she married Percy Shelley, one of the most famous poets of the day. In such an environment, literary excellence was a given.
On vacation in Geneva during the dreary, cold summer of 1816, Mary, her future husband, Lord Byron and John Polidori had a contest to come up with the best ghost story. While Percy Shelley's ghost story collection was only published posthumously, and Byron's vampire novel was abandoned, Polidori ended up writing a story called The Vampyre. (The titular vampire, Lord Ruthven, was heavily inspired by Byron's own brooding image) But Mary's story, which came to her in a dream, became an 1818 novel that essentially invented modern science fiction and introduced one of literature and pop culture's most enduring characters.
First-time readers of the novel will be surprised just how little it resembles any of the film versions of the story. (Kenneth Branagh's came close, but screwed a few things up). The novel has a double framing structure in which we are told Victor Frankenstein's story through sea Captain Robert Walton's to his sister Margaret (critics have noted that the reader is in essence taking a woman's role). Walton finds Victor near the North Pole, almost frozen to death,upon which he hears Victor's shocking tale.
Shelley took from the popular scientific theories of the time, most notably the idea that electricity could be used to want to reanimate dead tissue.The actual process is rather vague (no hunchbacked assistant or electric machinery here) but the creature is described in gruesome detail: enormous, with pale, translucent skin, yellow eyes and long black hair. Horrified,Victor abandons the creature and suffers a complete breakdown..
Months later, the creature returns, and mayhem, of course, ensues. Yet this isn't the monstrous mute of most movie adaptations. The creature can talk and has taught himself to read (most notably Paradise Lost, whose Satan has echoes in the creature). For all his brutal violence, the creature is more interesting and even sympathetic than the indecisive, naive Victor.
Gothic horror was already a popular genre at the time; Matthew Lewis' The Monk, an especially lurid supernatural novel, was a huge hit at the time. But Frankenstein took the revolutionary step of making the monster scientific rather than occult-oriented. Mary Shelley grew up in a household without much reverence for religion, but she clearly saw danger in tampering with nature. The story is tragic for both Victor and his creation.
But is it scary? Hell yeah. There are some gruesome murders, but the terror comes more from Victor's utter sense of dread at his own creation and the implications of its existence. (At one point Victor imagines a race of ghouls overrunning the Earth, predating the modern zombie by over a century).
Frankenstein's creature may lack the sex appeal of Dracula, but he has remained one of the icons of horror for centuries in large part to Mary Shelley's nightmare. Mary Shelley went on to write other books, most notably the post-apocalyptic novel The Last Man, but she'll always be remembered for creating the good doctor and his creature.