G. E. Moore (1873-1958) was a distinguished and hugely influential English philosopher who was educated and taught at Cambridge University. He was, with Bertrand Russell, Wittgenstein, and (before them) Frege, one of the primary inspirations of the analytic philosophy tradition that now predominates in the English-speaking world. Moore was best known for his advocacy of common sense, his ethical non-naturalism, and his very clear, circumspect writing style. He was very much a "philosopher's philosopher"--influential among and greatly respected by other philosophers, but relatively unknown to nonphilosophers (unlike his friend and colleague Russell).
Moore's most famous essays are "The Refutation of Idealism," "A Defence of Common Sense," and "A Proof of the External World," each of which can be found in his collection of papers, Philosophical Papers.
Moore is also well-known for the so-called "open question argument," which is contained in his (also greatly influential) Principia Ethica. The Principia is one of the main inspirations of the movement against ethical naturalism and is partly responsible for the twentieth-century concern with meta-ethics.