“I am pouring forth a penny dreadful,” Robert Louis Stevenson wrote a friend in the autumn of 1885. “It is dam dreadful.”

The pulp piece the Treasure Island author was referring to was the Strange Case of Dr. Jekyll and Mr. Hyde, a novella about a man with a (now notorious) split personality: the good Dr. Jekyll and the terrible Mr. Hyde. The book taps into fundamental truths about human nature, and has influenced everything from the detective story to the Incredible Hulk. Here’s what you should know.

1. The story for Dr. Jekyll and Mr. Hyde came to Robert Louis Stevenson from a dream ...

Stevenson had long been fascinated with split personalities but couldn’t figure out how to write about them. Then one night, he had a dream about Dr. Jekyll and Mr. Hyde. “In the small hours of one morning ... I was awakened by cries of horror from Louis,” his wife Fanny said. “Thinking he had a nightmare, I awakened him. He said angrily: ‘Why did you wake me? I was dreaming a fine bogey tale.’”

Stevenson later elaborated on the dream in an essay called “A Chapter On Dreams”: “For two days I went about racking my brains for a plot of any sort,” he wrote, “and on the second night I dreamed the scene at the window, and a scene afterward split in two, in which Hyde, pursued for some crime, took the powder and underwent the change in the presence of his pursuers. All the rest was made awake, and consciously[.]”

2. ... and it may have been influenced by a cabinet from his childhood.

Many historians speculate that the duality of Dr. Jekyll and Mr. Hyde was inspired by an 18th-century Edinburgh cabinet maker named Deacon Brodie, a respectable town councilor and an extremely successful craftsman. Brodie’s job gave him access to the keys of the rich and famous, which he made copies of in order to rob them at night. After a string of heists, he was eventually caught and hanged (according to legend, on a gallows that he helped design).

Brodie’s story fascinated the people of Edinburgh, including Stevenson—even though the thief died more than 60 years before Stevenson was born. The future writer grew up with a Brodie cabinet in his room, and in 1880, he cowrote a play called Deacon Brodie, or the Double Life. But the cabinet, and the man who built it, may have influenced Jekyll and Hyde, too: In 1887, Stevenson told an interviewer that the dream that inspired his story involved a man “being pressed into a cabinet, when he swallowed a drug and changed into another being.”

3. Dr. Jekyll and Mr. Hyde was written in just a few days.

A lifelong invalid, Stevenson was sick with tuberculosis when he wrote the famous tale. He’d recently suffered a lung hemorrhage and was under doctor’s orders to rest and avoid excitement. Still, that didn’t stop him from cranking out the first draft of the 30,000-word novella in somewhere between three and six days flat, and then a second, rewritten draft in another meager three days (more about that in a minute).

4. Stevenson may have been on cocaine when he wrote it.

In the book, Dr. Jekyll takes a drug from a chemist that turns him into another person. He likes it—until he loses control of the drug. Stevenson may have been drawing from personal experience. It's been reported that he was prescribed medicinal cocaine to treat his hemorrhage (it was discovered in the 1880s that cocaine tightens blood vessels), and that the inspired dream for the story occurred during a cocaine-fueled slumber. Stevenson later professed an affection for the drug, and his wild writing stint is consistent with someone on cocaine. Then again, it’s also consistent with a man faced with financial problems (as Stevenson was) and his own mortality, swept up by inspiration and a great idea.

5. The first draft of Dr. Jekyll and Mr. Hyde was destroyed ...

According to one version of events, after reading the manuscript for Jekyll and Hyde, Fanny criticized its failure to successfully execute the story’s moral allegory (among other things). Fanny later recounted that she then found her husband sitting in bed with a thermometer in his mouth. He pointed to a pile of ashes in the fireplace, revealing he’d burned the draft. “I nearly fainted away with misery and horror when I saw all was gone,” she wrote.

6. ... possibly by Stevenson’s wife, Fanny.

There are actually several theories as to how the first draft went up in flames. In 2000, a letter found in an attic revealed more of Fanny’s thoughts on the book, and her mysterious role in the manuscript’s burning. “He wrote nearly a quire of utter nonsense,” she wrote to friend and poet W.E. Henley. “Fortunately he has forgotten all about it now, and I shall burn it after I show it to you. He said it was his greatest work.” The artifact contradicts Fanny’s previous recounting, as well the one her son told of Stevenson burning the manuscript after he and Fanny got in a fight. In any case, Stevenson spent six weeks revising the book before it was ready for publication.

7. Dr. Jekyll and Mr. Hyde was an immediate success.

Dr. Jekyll and Mr. Hyde sold 40,000 copies in six months, and soon there were more than 250,000 pirated copies in North America. People seized on the moral message of the story. They wrote about it in religious newspapers and preachers gave sermons about it in churches. Within a year, there was a play based on the book, and soon there were productions in Scotland and the United States. It was Stevenson’s most successful novel.

8. Stevenson was adamant that the book wasn’t about sexuality.

The most common interpretation of Dr. Jekyll and Mr. Hyde is that Mr. Hyde’s corruption comes from sexual activity in the form of assault, promiscuity, or homosexuality. (Remember, it was the Victorian era.) In a private letter to the New York Sun, Stevenson wrote that Mr. Hyde was not “a mere voluptuary. There is no harm in a voluptuary and … none—no harm whatever—in what prurient fools call ‘immorality.’” He added that Hyde was a hypocrite, “the essence of cruelty and malice, and selfishness and cowardice.”

9. An actor portraying the titular double role was accused of being a killer.

In 1888, a stage play of Dr. Jekyll and Mr. Hyde opened starring Richard Mansfield as Jekyll/Hyde. The audience raved about Mansfield’s performance, finding it “thrilling and terrifying in equal measure,” according to Salon.

Then, two days after the play opened, Jack the Ripper began his infamous killing spree in London. It wasn’t long before people started connecting him to the stage adaptation, with some suggesting that the serial killer’s mind was poisoned by the play. Still others thought that Mansfield himself was the killer—and letters in the newspaper suggested that Mansfield was too good at playing a killer not to be Jack the Ripper.

10. A cinematic special effect used in the film was a secret for decades.

By 1931, Dr. Jekyll and Mr. Hyde had already been adapted for film 24 times, including a 1920 film starring John Barrymore. But the 1931 version impressed critics with its transformation scene, in which the actor Fredric March—who later won an Academy Award for his performance—turns into Hyde. The secret of how director Rouben Mamoulian shot the scene wasn’t revealed until the 1970s: It was done with colored make-up and matching colored filters, which were removed or added to the scene to change March’s appearance. Since the film was in black-and-white, the color changes didn’t show. You can watch the scene above.

11. The pop culture footprint of Dr. Jekyll and Mr. Hyde is everywhere.

There are few books that have seeped more deeply into popular culture than Dr. Jekyll and Mr. Hyde. Beyond movies, there have been cartoon adaptations with Mighty Mouse and Bugs Bunny. Stan Lee once said that along with Frankenstein, Dr. Jekyll and Mr. Hyde helped to inspire The Incredible Hulk. There’s a musicals—1990’s Jekyll & Hyde—and a 1988 Nintendo game. Comedies and parodies abound, including Stan Laurel’s silent-but-amusing spoof Dr. Pyckle and Mr. Pride (above), which holds up pretty well.

A version of this story ran in 2015; it has been updated for 2023.

This article was originally published on www.mentalfloss.com as 11 Strange Facts About ‘Dr. Jekyll and Mr Hyde’.