In 1982, Stephen W. Hawking decided to put his years of groundbreaking research in theoretical physics into book form. His goal, he said, was to “explain how far we had come in our understanding of the universe,” and how humankind might be close to finding a unified theory of the cosmos.

It would not be a dry, technical work designed for experts. Hawking wanted readers. He contacted a literary agent and said he hoped to write “the sort of book that would sell in airport bookstores,” as he recalled in the Wall Street Journal in 2013.

“He told me there was no chance of that,” Hawking said. “It might sell well to academics and students, but a book like that couldn’t break into bestseller territory.”

Several years and many rewrites later, Hawking’s “A Brief History of Time” defied all those expectations. The first run sold out in the United States in a matter of days, and soon the 200-some-page account of the origin and fate of the universe was flying off the shelves worldwide. It spent 147 weeks on the New York Times bestseller list and a record-breaking 237 weeks on the Times of London bestseller list. To date, more than 10 million copies have been sold, and the book has been translated into dozens of languages.

How many people read the book from cover to cover remains a running joke, which even Hawking found humorous. The number of people who read the book and understood it is also a matter of debate.

But “A Brief History of Time” launched Hawking, who died Wednesday at 76, into popular culture. Already renowned in academia for his contributions to cosmology, Hawking grew into a cultural icon and one of the world’s most celebrated science communicators.

What exactly was it that gave “A Brief History of Time” such sweeping popular appeal? It’s hard to pinpoint any one thing. Black holes, superstrings and deep dives into the finite yet boundless nature of the universe don’t necessarily make for great airplane reading. Hawking himself wrestled with the question long after the book’s 1988 publication. “It’s difficult for me to be objective,” he wrote in the Wall Street Journal.

The manner in which Hawking broke down complex concepts in theoretical physics, along with his deft use of humor and analogy, clearly won over many readers who might have otherwise found themselves intimidated by such material.

Upon publication, Hawking’s work was described by the New York Times as “a jaunty and absolutely clear little book” that shared his ideas about the universe “with everyone who can read.”

“His book is a rare sharing of confidence by a scientist with uncommon courage, a dazzling vision and an impish sense of humor,” the review read. The Guardian offered similar praise years later, calling it “succinct, entertaining and brilliantly lucid.”

On Goodreads, the social book-review database, many users give it high marks for its plain language, wit and overall simplicity. Some say Hawking’s writing style makes them feel as though they can still learn, even if they don’t grasp everything.

“Isn’t it amazing that a person can read a book like A Brief History of Time by Stephen Hawking and come away feeling both smarter and dumber than before he started,” one user wrote. It was “written with accessibility in mind, knowing full well idiots like me wouldn’t buy it, read it or recommend it if it were impossibly dense.”

Of course, the book has its skeptics, too. Among them are The Washington Post’s Charles Krauthammer, who, after reading it twice, found it “entirely incomprehensible.” (Krauthammer, by the way, is a Harvard-trained physician.)

Editorial decisions by Hawking and his publisher also appear to have helped bring in a broad audience. Writing in the Journal, Hawking recalled how his editors put him through round after round of rewrites, sending him long lists of objections and questions. They also limited him to one mathematical equation, Albert Einstein’s famous E = mc², saying every additional formula would slash sales.

One editor, Peter Guzzardi of Bantam Books, pressed Hawking for numerous rewrites to make the book more understandable to nonscientists, Hawking wrote in the Journal.

Guzzardi wrote in the Guardian Tuesday that Hawking’s original manuscript was 100 pages of “extremely dense” material. He remembered how he pushed Hawking to simplify things without dumbing them down, with the aim of crafting a work that was “scientifically accurate without being impenetrable to the general reader, someone like me.”

“My primary contribution to the book,” Guzzardi said, “was to doggedly keep asking Stephen questions, not giving up until I understood what he intended to convey.”

Hawking recalled in the Journal: “At times I thought the process would never end. But he was right: It is a much better book as a result.”

Guzzardi can also be thanked for the book’s title. Hawking had originally proposed “From the Big Bang to Black Holes: A Short History of Time.” Guzzardi changed it to the more concise “A Brief History of Time,” which spawned endless parodies and derivatives, including “A Brief History of Thyme.”

“It was a stroke of genius and must have contributed to the success of the book,” Hawking wrote.

Another important decision came during the proofing stage. Hawking considered cutting what has become the book’s most famous quote: that if humankind did discover a unified theory of the universe, “we would know the mind of God.” Had the line been left out, “the sales might have been halved,” wrote Hawking, a self-described atheist.

Hawking’s personal struggle with a disease similar to amyotrophic lateral sclerosis, or Lou Gehrig’s disease, may have also created an intrigue that drew in readers. His book barely touches on the condition that left him almost completely paralyzed for most of his life, but for some readers the subtext of “A Brief History of Time” was a human interest story about a genius who overcame his disability. Multiple reviews from the time touch on this. Hawking said in the Journal that it probably helped sales, but he signaled he was uneasy with such a reading.

Hawking and others have long joked that many people purchased his book because it made them look smart but never bothered to read it. “He agreed that the book, ‘Brief History of Time,’ was probably the least-read, most-bought book ever,” Leonard Mlodinow, a physicist at the California Institute of Technology, told NPR.

Hawking, well-known for his wry sense of humor and willingness to take a joke, said he was sure this was true for some people. But he was just as confident that a range of readers had waded all the way into his work. He said he was flattered to see the Independent once compared his book to the cult classic “Zen and the Art of Motorcycle Maintenance.”

“I hope that, like ‘Zen,’ it gives people the feeling that they need not be cut off from the great intellectual and philosophical questions,” he wrote in his 2013 Journal commentary.

“Even now,” he added, “I get a pile of letters every day, many asking questions or making detailed comments that indicate the writers have read the book, even if they do not understand all of it.”

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