It could have something to do with the age he was diagnosed. Most people develop the illness, which impairs the function of nerves and muscles, between 55 and 75, the National Institute of Neurological Disorders and Strokes (NINDS) reports. Those diagnosed with the disease at a younger age tend to live longer, according to ALS studies.
Genetics may also play a role in Hawking's lengthy survival, Live Science reported.
There is no cure for ALS, but there are several FDA-approved drugs that can extend life expectancy by about six months, according to Live Science, which doesn't explain Hawking's long survival with the disease.
>> Related: Gene Wilder's widow opens up about actor's battle with Alzheimer's Disease
While the illness may have forced Hawking into a wheelchair and left him voiceless with his only means of communication through a computer, it never slowed down his intellect or genius and, if anything, seemed to accelerate his scientific drive and ambition. He spent 30 years as a professor at Cambridge, and, in addition to his scientific accomplishments, he's also a prolific writer and penned one of the most iconic books of the 20th century "A Brief History of Time."