In 1907 Albert Einstein realized that his Theory of Special Relativity is missing something that is not in accordance with the reality that we live. So he started thinking about how the nature works, mainly in time and space. After few years he discovered new theory called Theory of General Relativity.
The main idea behind his relativity is space and time are parts of the same thing called Space-Time. While thinking of this fabric of space time Einstein prove that this space time can be curved. Massive objects such as our sun can curve the space-time that can be noticeable during the solar eclipse. Sir Arthur Eddington, an English astronomer, proved General Relativity is correct during a solar eclipse which happen In 1919.