John Locke was an English philosopher and physician who is widely regarded as one of the most influential Enlightenment thinkers. He is best known for his work on the social contract theory, which he outlined in his book 'Two Treatises of Government'. Locke argued that individuals have natural rights to life, liberty, and property, and that governments should be formed to protect these rights. He also argued that governments should be limited in their power and that citizens should have the right to overthrow them if they become oppressive.