If ever a human being seemed capable of living forever, that human was Stephen Hawking. In 1963, when Hawking was twenty-one, he was diagnosed with amyotrophic lateral sclerosis, the degenerative neurological disorder, and given three years to live; he died this past Wednesday, at the age of seventy-six. For five decades, he used an electric wheelchair and, as the years progressed, had an ever-shrinking range of motion. Toward the end, only the twitch of a cheek muscle, processed through a computer interface with a digital voice, provided an outlet for the churning, often playful mind inside. To the eye alone, he was a rumpled suit on wheels, fathoming the unfathomable.

“Hawking has become a kind of a ‘brain in a vat,’ ” the anthropologist Hélène Mialet wrote, in 2013, on Hawking’s seventy-first birthday. “In some ways Hawking is, to borrow from Obi-Wan referring to Darth Vader, ‘more machine now than man.’ ” Hawking embraced this perception. In an episode of “Star Trek: The Next Generation,” one of his dozens of pop-culture cameos, he was a hologram playing cards with Einstein and Newton. On “The Simpsons”—which Hawking appeared in several times and called “the best show on American television”—Homer refers to Hawking’s character as Lisa’s “robot buddy.” On “Futurama,” Hawking was an everlasting head in a jar, a role he reprised, last year, with heads-in-jars Bill Nye, Neil deGrasse Tyson, and George Takei in the video trailer for the “Futurama” smartphone game. He was not a fully disembodied voice, but he was moving steadily in that direction.

In a parallel universe, would a non-disabled Hawking have become as famous? Certainly his condition did not impede his work; it may even have sharpened it. “All my life I have lived with the threat of an early death, so I hate wasting time,” he told the Guardian, in 2013. His scientific contributions were as profound as they were hard to grasp. Like many theoretical physicists, Hawking yearned to wed quantum physics, the spooky science of the subatomic realm, to Einstein’s relativity and the weird physics of gravity at cosmic scales. He managed to do so in the case of black holes, concentrations of matter so dense that, at least according to classical physics, not even light can escape their gravitational grip. In a 1984 paper, Hawking showed that, theoretically, under quantum mechanics, matter—known as Hawking radiation—actually could escape a black hole.

Hawking’s career spanned a remarkable awakening in astronomy and astrophysics. New telescopes and satellite-borne instruments enabled scientists to observe stars from the earliest stages of cosmic evolution and to probe the structure of the cosmic microwave background, the afterglow of Big Bang radiation that suffuses the universe. The study of our cosmic beginning, once as vaporous as astrology, became an experimental science; cosmologists moved from basement warrens into grand sunlit offices in Cambridge, Pasadena, and Manhattan. Black holes were part of this story. Einstein theorized their existence in 1916; the first one was observed in 1971. Now we know that they are everywhere, by the billions, and that a supermassive black hole lies at the heart of probably every galaxy, including our own Milky Way. Hawking demonstrated that black holes weren’t necessarily the final stop for matter: they could leak, dissolve, explode.

Perhaps Hawking’s greatest achievement is that he could make all this accessible, or at least approachable. His first book, “A Brief History of Time,” published on April Fool’s Day of 1988, has sold more than ten million copies and spent months on the Times best-seller list. It is sometimes described as the most popular book that nobody has actually read, although reading even the complicated parts is a treat. Hawking acknowledged its limitations by subsequently publishing “The Universe in a Nutshell,” “A Briefer History of Time,” and “The Illustrated Brief History of Time,” among other books. “Even if you only look at the pictures and their captions, you should get some idea of what is going on,” Hawking wrote in the foreword to the illustrated version.

Before Hawking, the great popularizer of space was Carl Sagan, who wrote the introduction to “A Brief History of Time.” Sagan’s cosmos was about the contents—the “worlds of ice and stars of diamond,” the “awesome machinery of nature”—and the journey through them, narrated with windblown hair and ponderous elocution. Hawking got us comfortable with the mathematical fabric, or at least with the fact of it; he made it possible for us to casually mention Euclidean space-time and gravitational fluctuations at dinner parties, even if we weren’t a-hundred-per-cent certain what we meant. That lack of certainty was unavoidable, even necessary. The true nature of our universe is strange as hell when you get right down to it, and all of our landlocked metaphors ultimately fail in their attempts to describe it. The only language that comes close is math, a math that is still being invented by the smartest among us.

Maybe that’s where Hawking’s physical condition was helpful, to us if not to him. Static and computerized, he was an otherworldly messenger, almost transparent to the viewer; it was easier to concentrate on his bizarre message without the usual distracting theatre of personality. But he was also, unmistakably, the essence of being—fragile, resilient, witty, dogged in pursuit of the greatest mystery. He lived at the intersection of two equally absurd realms, the cosmological and the physiological, and was eager to serve as a portal between the two. The fabric of space-time was less alarming to consider when it was described by a person who seemed to be woven directly from it.

Of course, Hawking was entirely human. As a kid, he did kid stuff: he rode his bike, played board games, took apart clocks and radios, built and set off fireworks with friends. At Oxford, bored and unchallenged, he joined the University College Boating Club as a coxswain. (He “had a daredevil way of sometimes steering his boat through gaps so narrow that the shell returned to the boathouse with its blades damaged,” a fellow-boatsman recalled.) He travelled to Antarctica and Easter Island, descended in a submarine, and flew in zero gravity. In 2014, he offered a scientific formula—inaccurate, ultimately—for how England could win the World Cup that year. He married twice and is survived by three children and a grandson.

And his genius, though singular, was not solitary. Mialet, the anthropologist, spent several years trailing Hawking for her book “Hawking Incorporated.” With the phrase “a brain in a vat,” she meant not that Hawking was an oddity but that he was perhaps the purest example of ordinary science: one node in a network of conversations and like minds, part of and buoyed by a living fabric of people, technologies, and ideas. “He is what I call a distributed centered-subject,” she wrote in Wired, in 2013. “It’s precisely because of his disability that we get to see how all scientists work . . . and how the entire world will work one day.”

Hawking described Homer Simpson approvingly as a guy who “is always trying to get something for nothing.” That’s the universe in a nutshell. According to Hawking, tiny quantum fluctuations in space-time may have become the seeds from which stars, galaxies, life, and intelligence emerged—perhaps more than once. “Science predicts that many different kinds of universe will be spontaneously created out of nothing,” he told the Guardian. “It is a matter of chance which we are in.” And, inevitably, something eventually becomes nothing again. Hawking entertained the possibility of eternal life, but he didn’t seem to yearn for it. “I think the brain is like a program in the mind, which is like a computer, so it’s theoretically possible to copy the brain on to a computer and so provide a form of life after death,” he told the Guardian. But, he added, “this is way beyond our present capabilities. I think the conventional afterlife is a fairy tale for people afraid of the dark.” A black hole is coming for us all, but with luck, and theory, a little bit of us may escape and radiate.