If you look up the word "chin" in the encyclopedia, you will read about Kirk Douglas. This isn't an exaggeration or a figure of speech: Douglas is literally named as an example of someone with a chin in the Oxford University Press entry for the mandibular arch.

It makes sense: there have been few chins in human history as noteworthy as Douglas'. When the actor died at the extraordinary age of 103 on Wednesday, obituaries seemed to mourn the loss of his dimple as much as his talent. "That famously dimpled chin, which you'd never believe on a statue, nonetheless gave the Hollywood icon a granite jaw that served him well as a leading man for more than 60 years," wrote Vanity Fair. "When you hear his name, so crisp and ramrod strong (Kirk!), you think, at first, of how he looked: the jutting chin with a dimple that made it unlike all other jutting chins," gushed Variety. The Los Angeles Times chose to describe the actor as a "dimple-chinned screen icon who was known for bringing an explosive, clenched-jawed intensity to a memorable array of heroes and heels."

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Of course chins, being at the lower center of our faces, have an outsized effect on perceived attractiveness, for better or worse. Curiously, humans are actually the only animal that have jutting lower jaws; "even chimpanzees and gorillas, our closest genetic cousins, lack chins," writes The Smithsonian, noting that the great apes' jaws slope down and back from their teeth instead of protruding forward. While researchers aren't sure why exactly humans have chins in the first place — even Neanderthals didn't have them — one hypothesis is that they were possibly a sexually selective feature that factored unconsciously into our choice of mates. These days, though, it's not so unconscious: Vulture has ranked Batmans by their chins, and BuzzFeed once ran a list of the Most Important Jawlines of 2014.

Despite being best known for portraying a rakish Spartacus in Stanley Kubrick's 1960 epic of the same name, Douglas' bullseye on his jaw wouldn't have been considered attractive 2,000-odd years ago. "In images whose beauties were of a lofty cast, the Greek artists never allowed a dimple to break the uniformity of the chin's surface," claimed Johann Joachim Winckelmann in The History of Ancient Art Among the Greeks in 1764, adding that "when, in drawings made from them, the lower part of [the chin] seems, as it were, to be pinched in ... it may justly be suspected that some modern ignorant hand has been attempting to improve upon them." In other words, dimples like Douglas', while left up to the mercy of genetics, have come and gone in popularity; the screen actor just happened to be born at the right time for his maximalist jawline to be in fashion.

Even by the standards of the time, though, when masculine icons from Batman to Clark Gable boasted clefts, Douglas was an extreme. "When I made my first picture [The Strange Love of Martha Ivers in 1946] with Barbara Stanwyck, the director wanted me to fill it in and I said 'listen, this is what you get.' I didn't cave," Douglas told The Telegraph in 2016. It was a decision that would have a lasting impact; as Douglas began to collect more on-screen roles, directors and agents realized they could use his dimple to their advantage, alternating between emphasizing it as a trait of a classical (if anachronistic) hero, or to accentuate the look of a tougher sort, like his character in Champion. As the Financial Times put it, regardless of if he was playing a good guy or a bad guy, "the Kirk jaw was made for clenching."

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It was also made for exaggerating. Artists leaned into depicting Douglas' distinctive jaw, but the actor never minded; in addition to the customary hand and foot prints outside the TCL Chinese Theater in Hollywood, he jokingly left behind an imprint of his chin as well. The body part was also a favorite topic of conversation in interviews: "It's not really a dimple, it's a hole in the chin," a bearded Douglas once told Dick Cavett, who quipped in response, "well I know if we could see it, it'd be the most cleavage we've had on the show in a long time." Seemingly everyone had questions about how he navigated shaving the thing. Later, when Douglas' grandson, Dylan, was born in 2000, The New York Post announced "NEWBORN HAS THE DOUGLAS DIMPLE" with the same drama as Rafiki holding up Simba to the savannah. Subsequent male actors with head-turning chins rode on the coattails of his success, from John Travolta to Simon Cowell. Nevertheless, on the occasion of Douglas' 100th birthday in 2016, The New Yorker declared that "the cleft in the Douglas chin is, with the exception of the Grand Canyon, the most popular natural rift in America."

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But physical trends come and go; just as Douglas' passing marks the loss of one of the last remaining legends of the Golden Age of Hollywood, so too do we lose one of the great chins of history. These days, plastic surgery websites advertise procedures to smooth out one's jawline: "Although chins with a dimple were once more popular, these have largely gone out of fashion, and some patients have preferred to have their dimple reduced, often with the use of fillers," cosmetic surgeon Dr. Julian De Silva told The Daily Mail in 2017.

Douglas, though, was nothing if not a titan of the industry, and he didn't make over 90 movies, many of them masterpieces of classic Hollywood cinema, by relying on his facial structure alone. To quote Angelo Dundee, a boxing instructor who coached Muhammad Ali, "You can't train a chin." The mandible, just like stardom, is elusive, innate, impossible to capture with words. You either have it or you don't.