Albert Einstein (14 March 1879 – 18 April 1955) was a German-born physicist who developed the general theory of relativity. He started his professional life as a patent clerk, and in his spare time, honed his scientific skills publishing numerous papers that challenged conventional thinking. Best known for his mass–energy equivalence formula E = mc2, Einstein has made numerous contributions to theoretical physics. It was his brilliance that led to the invention of the atomic bomb, and the defeat of the Nazis in World War 2. He understood that mass and energy are really the same thing - two sides of a same coin - and that mass could be transformed into energy and vice versa. He was able to give an exact value to the amount of energy that could be released from any given mass. His equation sums up one of the most powerful truths of the universe. By his equation, there is enough energy contained in an amount of mass equal to a glass of water, to supply power to the whole of London city for a whole week.