David Hume
David Hume was a prominent figure of the 18th century's Scottish Enlightenment, known especially for his skepticism and rejection of theism. His early philosophical work, A Treatise of Human Nature, first published anonymously around 1739, is considered a standard of Western philosophy. Hume, taking his cue from John Locke, rejected metaphysics in favor of a focus on the empirical method -- the idea that experience and observation should be the foundation of all human knowledge. His dismissal of religion kept him from getting desired academic posts, but Hume became well known for his philosophical works and the controversies they caused, and his multi-volume History of England (1754-62) made him financially secure in his later years. Like his friend Adam Smith, Hume wrote about politics, economics and the moral obligations of government. Some of his most famous works are posthumously published works on religion, including A Natural History of Religion and An Enquiry Concerning the Principles of Morals.
Extra credit: Hume famously helped Jean-Jacques Rousseau out of Switzerland, then set him up at a house in England. Rousseau ended up accusing Hume of being part of a plot against him, and the two had a public falling out, with Hume publishing his defense as A Concise and Genuine Account of the Dispute Between Mr. Hume and Mr. Rousseau: With the Letters that Passed Between Them During Their Controversy (1766).