John Locke was an English philosopher and physician, widely regarded as one of the most influential of the Enlightenment thinkers and commonly known as the "father of liberalism". Considered one of the first of the British empiricists, following the tradition of Francis Bacon, Locke is equally important to social contract theory. His work greatly affected the development of epistemology and political philosophy.

His writings influenced Voltaire, Jean-Jacques Rousseau, and many Scottish Enlightenment thinkers, as well as the American Revolutionaries. His contributions to classical republicanism and liberal theory are reflected in the United States Declaration of Independence. Internationally, Locke's political-legal principles continue to have a profound influence on the theory and practice of limited representative government and the protection of basic rights and freedoms under the rule of law.

Locke's philosophy of mind is often cited as the origin of modern conceptions of personal identity and the psychology of self, figuring prominently in the work of later philosophers, such as Rousseau, David Hume, and Immanuel Kant. He postulated that, at birth, the mind is a blank slate, or tabula rasa. Contrary to Cartesian philosophy based on preexisting concepts, he maintained that we are born without innate ideas, and that knowledge is instead determined only by experience derived from sense perception, a concept now known as empiricism. Locke is often credited for describing private property as a natural right, arguing that when a person—metaphorically—mixes their labour with nature, resources can be removed from the common state of nature.