Stephen Hawking died Tuesday at his home in England. He was 76. Hawking was known for his work on the universe and black holes, and for his wheelchair-bound persona. He was diagnosed with ALS at age 22, and lived with the disease for more than 50 years. It left him unable to move most of his body. He was dependent on technology for just about everything, including his ability to speak, but his brain was undiminished.