David Kellogg Lewis (September 28, 1941 - October 14, 2001) is considered to have been one of the leading analytic philosophers of the latter half of the 20th century. Born in the United States of America, he taught there (at UCLA and then Princeton) for his career but is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years. He is most famous for his theory of modal realism but also made ground-breaking contributions in philosophy of language, philosophy of mind, general metaphysics, epistemology, and philosophical logic.

Lewis was born in Oberlin, Ohio, to a Professor of Government at Oberlin College and a distinguished medieval historian. He was known later in life for his formidable (even intimidating) intellect; this intelligence was already manifest during his years at Oberlin High School, when he attended college lectures in chemistry. He went on to Swarthmore College, and spent a year at Oxford (1959-1960), where he was tutored by Iris Murdoch and attended lectures by Gilbert Ryle, H. P. Grice, P. F. Strawson, and J. L. Austin. It was his year at Oxford that played a seminal role in his decision to study philosophy, and which made him the quintessentially Analytic philosopher that he would be for the rest of his life. Lewis went on to receive his Ph.D from Harvard in 1967, where he studied under W. V. O. Quine. It was there that his connection with Australia was first established when he took a seminar with J. J. C. Smart, a leading Australian philosopher. "I taught David Lewis," Smart would say in later years, "Or rather, he taught me."

Lewis's most important works include Convention (1969), which used concepts of game theory to analyze the nature of linguistic conventions; Counterfactuals (1973), which astonished the philosophical world with a ground-breaking analysis of counterfactual conditionals in terms of the theory of possible worlds; and On the Plurality of Worlds (1986), which fleshed out and defended the theory of modal realism (a label that he was by then regretting, but with which his theory was stuck) which he had advanced in Counterfactuals. His final monograph, Parts of Classes (1991) sketches a reduction of set theory to mereology. He also published five volumes of collected papers covering a remarkably wide range of topics.

Lewis suffered from severe diabetes for much of his life, which eventually grew worse and led into kidney failure. In July of 2000 he received a kidney transplant from his wife Stephanie. The transplant allowed him to work and travel for another year, before he died suddenly, and unexpectedly, from further complications of his diabetes, on 14 October 2001.