David Kellogg Lewis was a 20th century philosopher. Lewis taught briefly at UCLA and then at Princeton from 1970 until his death. He is also closely associated with Australia, whose philosophical community he visited almost annually for more than thirty years. He has made ground-breaking contributions in philosophy of language, philosophy of mind, metaphysics, epistemology, and philosophical logic. He is probably best known for his controversial modal realist stance: that there exist infinitely many concretely existing and causally isolated parallel universes, of which ours is just one, and which play the role of possible worlds in the analysis of necessity and possibility.

-wikipedia