One of the world's most famous scientists, Professor Stephen Hawking, has died at the age of 76.
The British scientist was known for his work in physics, and he wrote several best-selling science books.
At the age of 22 Professor Hawking was given only a few years to live, after being diagnosed with a rare form of motor neurone disease.
Despite his illness, he continued to write books, make speeches and work as a scientist at the University of Cambridge.
Ricky's been looking back at his life.