John Locke (1632-1704) was a British philosopher now considered the father of classical liberalism. His writings inspired the authors of the Constitution of the United States of America, including the notions of personal sovereignty and a social contract. These notions are still apparent in modern American politics, which separates church from state and respects individual rights.
Locke studied medicine at the prestigious Christ Church school in Oxford. He became the personal physician for the man who would become the Earl of Shaftesbury, and later became involved in the Earl's political efforts after the Earl became Chancellor. Locke and Shaftesbury both fled England under suspicion of treason, spending time in both France and Holland.
It was in Holland that Locke wrote Two Treatises of Government. The first treatise addresses the "common sense" approach that God could not give divine rights to rule to a king alone, but rather gave rights to all individuals—specifically the rights of Life, Liberty, and Property. The second treatise outlined the social contract and the origins of individuals as free and equal in a state of nature. It is individuals who enter into a social contract to create and enforce laws by government.
These notions (among others) made Locke a hero for founding fathers such as Thomas Jefferson and had great influence on the shaping of the Declaration of Independence and US constitution.