Professor Stephen Hawking published many books tackling the fundamental questions about the universe and our existence. Picture: AP Photo/Markus Schreiber,

World-renowned British theoretical physicist Stephen Hawking, 76,  passed away on Wednesday, after a decades long battle with the motor neurone disease. 

Despite being diagnosed at 21 years old, Stephen is best known for his contributions to the fields of cosmology, general relativity and quantum gravity, especially in the context of black holes.

Over the years, Hawking has published many books tackling the fundamental questions about the universe and our existence. Here are six of his most popular books:

A Brief History of Time

Was there a beginning of time? Could time run backwards? Is the universe infinite or does it have boundaries? These are just some of the questions considered in an internationally acclaimed masterpiece by one of the world's greatest thinkers. It begins by reviewing the great theories of the cosmos from Newton to Einstein, before delving into the secrets which still lie at the heart of space and time, from the Big Bang to black holes, via spiral galaxies and strong theory. 

The Grand Design

When and how did the universe begin? Why are we here? What is the nature of reality? Is the apparent ‘grand design’ of our universe evidence for a benevolent creator who set things in motion? Or does science offer another explanation? 

In The Grand Design, the most recent scientific thinking about the mysteries of the universe is presented in language marked by both brilliance and simplicity.

The Universe in a Nutshell

In 200 highly illustrated pages, Hawking is pushing the frontiers of popular physics beyond relativity and quantum theory, past superstring theory and imaginary time, into a dizzying new world of M-theory and branes.

A Briefer History of Time

Although “briefer,” this book is much more than a mere explanation of Hawking’s earlier work. 

A Briefer History of Time both clarifies and expands on the great subjects of the original, and records the latest developments in the field—from string theory to the search for a unified theory of all the forces of physics. 

Thirty-seven full-color illustrations enhance the text and make A Briefer History of Time an exhilarating and must-have addition in its own right to the great literature of science and ideas.

Black Holes and Baby Universes

In his first collection of essays and other pieces - on subjects that range from warmly personal to the wholly scientific- Stephen Hawking is revealed variously as the scientist, the man, the concerned world citizen, and - as always - the rigorous and imaginative thinker. 

On the Shoulders of Giants

On the Shoulders of Giants tells a compelling story, using original papers from Einstein, Copernicus, Galilei, Kepler and Newton. Theoretical physicist Stephen Hawking explains how these works changed the course of science, ushering astronomy and physics out of the Middle Ages and into the modern world.