Stephen Hawking, the British theoretical physicist and cosmologist, has died, a spokesman for his family announced Wednesday. He was 76. Hawking died at his home in Cambridge. In a statement, his children, Lucy, Robert, and Tim called their father “a great scientist and an extraordinary man whose work and legacy will live on for many years.”

Hawking worked on black holes and quantum fluctuations, and his 1988 book A Brief History of Time sold more than 10 million copies and was translated to 40 different languages. Hawking had an early-onset form of amyotrophic lateral sclerosis (ALS) that progressed slowly over time, ultimately leaving him paralyzed, and he used a device in order to speak. He was diagnosed at 21, and expected to only live for two more years.