He was diagnosed with ALS at the age of 21, and was given less than three years to live. He went on to live over another half-century - obtained his PhD, continued his work in physics, got married twice, became Lucasian Professor of Mathematics at Cambridge, published a whole bunch of best-selling books, appeared in Star Trek: The Next Generation and The Simpsons, travelled all over the world, went up in a hot air balloon on his 60th birthday, went up on the Great Wall of China, and participated in zero gravity flight at 65, among other things. Because I can’t properly articulate my own feelings, I will instead quote Neil deGrasse Tyson: “His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure.” [He and his book A Brief History of Time entered my life when i was 14, and have been following his progress through life ever since, that I kind of expected him to live forever. (But perhaps this is true in an alternate universe).]