In the 203 years since Mary Shelley’s Frankenstein helped shape the horror genre as we know it today, there have been dozens of interpretations of Frankenstein’s Monster. For most of us, the version of the character that immediately comes to mind is the one from Universal’s classic 1931 film: Big green guy with a flat head and bolts in his neck who isn't much of a talker—which is a far cry from the yellow-skinned, chatty creature Shelley imagined. But if our popular idea of the Monster's appearance was dictated by a black-and-white movie, why is Frankenstein’s Monster so often depicted as being green?

To understand why the Monster looks the way he does today, it’s helpful to look at how he evolved after the 1818 publication of Frankenstein. Here’s how Shelley described him:

"His yellow skin scarcely covered the work of muscles and arteries beneath; his hair was of a lustrous black, and flowing; his teeth of a pearly whiteness; but these luxuriances only formed a more horrid contrast with his watery eyes, that seemed almost of the same color as the dun white sockets in which they were set, his shriveled complexion, and straight black lips."

The Monster first stepped off the page five years later, with playwright Richard Brinsley Peake’s 1823 stage adaptation Presumption, or the Fate of Frankenstein. Peake’s version of the Monster hews fairly close to the book (physically, at least), with the exception of his skin color. He’s described in the play’s script as having skin that’s “light blue or French gray.”

But Peake made a key change to the character: in his play, the Monster was mute. Due to the era’s strange theater licensing rules, only a few select companies, known as patent theaters, could legally perform traditional dramas; all others had to present what was known as illegitimate theater, or works that included elements such as burlesque, pantomime, puppetry, or musical performances. Peake has been dead for nearly 175 years, so we can’t ask him, but it’s often presumed that he made the creature mute to give the play a pantomime aspect that would allow it to be performed. (It was also Peake who introduced the character of the doctor’s assistant, Fritz, who would later come to be known in popular culture as Igor.) The popularity of Peake’s show probably helped cement the idea of a mute, not-yellow Monster in the minds of the public.

Other stage adaptations experimented with different skin colors for the creature, including green. But the definitive greening of Frankenstein’s Monster would take an additional 108 years, when legendary makeup artist Jack Pierce was tasked with designing the character for James Whale’s 1931 masterpiece Frankenstein. Pierce was a Greek immigrant who had spent years working his way up to the head of Universal’s makeup department. He was an artist and a visionary, and his work defined some of pop culture’s most famous characters. Besides his makeup applications for Dracula, Frankenstein, and The Mummy, Pierce created Conrad Veidt’s nightmarish grin in 1928’s The Man Who Laughs—a design that’s widely credited with influencing the Joker’s iconic rictus.

According to film historian David J. Skal’s indispensable book The Monster Show, Pierce’s creature design for Frankenstein was a combination of his own ideas and elements he borrowed from other interpretations of the Monster. Whale had imagined the creature’s protruding brow in sketches he made and showed to Pierce, and the electrodes in the Monster’s neck first showed up in a concept illustration by Universal poster artist Karoly Grosz. Pierce gave the monster his now-famous squared head because he imagined that the easiest way to install a new brain would be to make a single, straight cut across the top of the skull, removing the dome and essentially turning the skull into a box with a convenient lid.

As for Pierce’s decision to slather Boris Karloff with green makeup: That was both a creative choice and a technical consideration. The color sensitivity of the film stock used in the 1930s meant that certain shades of green would show up on screen as a ghostly white. Karloff’s green makeup, then, both tinted the actor’s skin to a cadaverous pallor and gave him a decidedly different complexion than the rest of the cast. Soon the green tint began to show up in promotional materials such as this poster, and thanks to the popularity of the film and its sequels—along with Universal’s allegedly aggressive copyrighting of Pierce’s design—Frankenstein’s Monster has been green ever since.

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