Albert Einstein (1879-1955) was one of the most respected scientists who ever lived. A theoretical physicist and philosopher of science, Einstein developed the special and general theories of relativity, applying the latter to map out the large-scale structure of the universe. He is most well-known for developing what is perhaps the most famous equation of all time: the mass-energy equivalence formula E = mc^2. Einstein was awarded the Nobel Prize in Physics in 1921. Later in life, he was a staunch supporter of American civil rights and an activist against the proliferation of nuclear weapons.

"Life is like riding a bicycle. To keep your balance you must keep moving."

Source: Letter to his son Eduard (5 February 1930), as quoted in Walter Isaacson's Einstein: His Life and Universe (2007), p. 367. (via Wikiquote)