His Greatest Works is a collection of Einstein’s writings spanning approximately 50 years, which Stephen Hawking edited and provided with commentary. What makes this collection so valuable is that it brings together short and long pieces by Einstein that focuses mainly on relativity.
Hawking kicks off with a paper from 1905. One which revolutionized our understanding of space and time. The Second paper, only just three pages long, proposing the equivalence of mass and energy: E=mc2.
For me this was the first time I really understand how this theory was developed and that it didn’t just fall out of the sky. I think this book is an excellent collection of important papers that certainly lives up to the title. However it is a very hard read and you would need a higher level of mathematics.