1. Stephen Hawking’s book A Brief History of Time was a surprising mainstream success.

Barack Obama and Stephen Hawking.
In 2009, President Barack Obama presented Stephen Hawking with the Presidential Medal of Freedom. | Somodevilla/Getty Images

Stephen Hawking rose to super-stardom with the publication of A Brief History of Time in 1988. His book took the dense material of his life’s work studying theoretical physics and turned it into “the sort of book that would sell in airport bookstores,” as he described it to a literary agent before writing. The book’s popularity was unprecedented—and not just for subjects that were normally limited to academic journals. It spent 237 weeks on the London Sunday Times's bestseller list, a record at the time; The New York Times's bestseller list for almost three years; and long ago surpassed 10 million copies sold. As a friend once remarked to him: He had sold more books on physics than Madonna had on sex.

2. Stephen Hawking's IQ wasn't something to brag about (according to him).

Stephen Hawking and wife Elaine Mason.
Stephen Hawking and his second wife, Elaine Mason, were married from 1995 to 2006. | Dave Benett/Getty Images

Stephen Hawking certainly had an impressive IQ, but he never divulged the number to the public. It’s unclear whether he even took the test in the first place. When asked about his IQ score in 2004, he told the interviewer, "I have no idea. People who boast about their IQ are losers."

3. Stephen Hawking died of ALS decades after doctors told him he would.

A photo of Stephen Hawking in his Cambridge office.
During his time as a professor at the University of Cambridge, Stephen Hawking worked in the Department of Applied Mathematics and Theoretical Physics. | Romano Cagnoni/Getty Images

Stephen Hawking was diagnosed with the disease amyotrophic lateral sclerosis (ALS) when he was a 21-year-old graduate student at Cambridge. The condition (also known as Lou Gehrig's disease) gradually degrades motor-neuron function, ending in death when patients are unable to breathe or swallow on their own. The insidious condition is fast-moving and debilitating, and doctors told Hawking he likely wouldn’t survive past age 25. Though he did lose most of his physical capabilities, the physicist outlived that prediction by decades. He died on March 14, 2018, at age 76.

4. Stephen Hawking may have had juvenile-onset ALS.

A photo of theoretical physicist Stephen Hawking.
Stephen Hawking is also known for appearances on TV shows like 'The Simpsons' and 'The Big Bang Theory.' | Michelly Rall/Getty Images

Experts aren’t sure what made Stephen Hawking an outlier in terms of his longevity, but his biology and the level of care he received were definitely factors. It’s also possible he had juvenile-onset ALS. The average ALS patient is diagnosed between ages 40 and 70, but patients with the juvenile-onset form of the disease start showing symptoms in their teens. This type progresses much slower than adult ALS, with patients sometimes living into their 60s. Hawking was no longer a teen when he got his ALS diagnosis, but he was young enough that experts have speculated he may have had the slower-moving of the two forms of ALS.

5. Stephen Hawking and his wife, Jane, had three children together.

Jane Hawking, the wife of Stephen Hawking.
Jane Hawking, Stephen Hawking's first wife, has a PhD in medieval Spanish poetry from Cambridge. | David Levenson/Getty Images

Stephen Hawking met his future wife Jane Wilde at a party the year before he was diagnosed with ALS. Despite his newly shortened lifespan and pessimistic outlook following the diagnosis, Jane wasn’t deterred from pursuing a relationship with him. The couple married in 1965, and the new union gave Hawking something to live for. Motivated by the need to support his family, he started showing a greater commitment to the scientific work he had abandoned, and ended up changing the world in the process.

During their marriage, Stephen Hawking and Jane had three children together:

  • Robert Hawking (1967)
  • Lucy Hawking (1970)
  • Timothy Hawking (1979)

The couple divorced in 1995, and Stephen Hawking went on to marry his second wife, Elaine Mason, the same year. In 2006, the couple divorced, and Hawking would remain single the rest of his life. Jane remarried in 1997.

6. Stephen Hawking’s voice generator predicted his speech.

Stephen Hawking in front of a screen giving a lecture.
Stephen Hawking's voice technology is now open source and available online. | Bryan Bedder/Getty Images for Breakthrough Prize Foundation

Stephen Hawking first started using a voice generator in 1985, following a surgery that rendered him totally speechless. This original synthesizer was controlled by a handheld device, but once Hawking lost control of his hands, he needed to figure something else out. The unique solution would be the system he used for the remainder of his life.

Called ACAT, short for assistive context-aware toolkit, it used infrared sensors attached to his glasses to detect muscle movements in his cheek. A cursor on his screen ran through the alphabet, and Hawking would move his face to stop it on a certain letter. Instead of forcing him to spell out sentences one letter at a time, the program used a highly personalized version of auto-suggest: He would select the first few characters of a word and then the computer would fill in the rest based on data gathered from his speech transcripts and books.

Intel has since made the ACAT technology open source and free to use.

7. The Stephen Hawking movie The Theory of Everything features his actual voice.

Eddie Redmayne played Stephen Hawking in the 2014 movie 'The Theory of Everything,' which earned the actor the Academy Award for Best Actor. | Tim P. Whitby/Getty Images

Stephen Hawking lived to see a biopic made about his life, which starred Eddie Redmayne, and even gave it his blessing. He visited the set of The Theory of Everything as it was being shot, and he was so happy with what he saw that he offered to lend his real “voice” to the film. Filmmakers had previously planned to use a synthetic replication of his voice, but the electronic voice in final cut is the same one used by Hawking. The physicist was apparently pleased with the final product: At a screening of The Theory of Everything, a nurse was seen wiping a tear off his face.

Famous Stephen Hawking quotes.

  • "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans. We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet."
  • “My disabilities have not been a significant handicap in my field, which is theoretical physics. Indeed, they have helped me in a way by shielding me from lecturing and administrative work that I would otherwise have been involved in.”
  • "I have noticed that even people who claim everything is predetermined and that we can do nothing to change it, look before they cross the road."
  • "Next time someone complains that you have made a mistake, tell him that may be a good thing. Because without imperfection, neither you nor I would exist."
  • "There is a fundamental difference between religion, which is based on authority, [and] science, which is based on observation and reason. Science will win, because it works."

Books by Stephen Hawking.

  • A Brief History of Time (1988)
  • Black Holes and Baby Universes and Other Essays (1993)
  • The Universe in a Nutshell (2001)
  • On the Shoulders of Giants (2002)
  • A Briefer History of Time (co-written with Leonard Mlodinow, 2005)
  • The Grand Design (co-written with Leonard Mlodinow, 2010)
  • My Brief History (2013)
  • Brief Answers to the Big Questions (2018)