 John Cook Wilson (1849–1915) was Wykeham Professor of Logic at New College, Oxford. His ideas are at the origin of ‘Oxford Realism’, a philosophical movement that flourished at Oxford during the first decades of the twentieth century. Although trained as a classicist and a mathematician, his most important contributions were to the theory of knowledge, where he argued that knowledge is factive in conjunction with the thesis that, as a state of mind, it is not definable in terms of belief—they share no ‘highest common factor’—and he thus rejected ‘hybrid’ and ‘externalist’ accounts of knowledge. He also argued for direct realism in perception, criticizing both empiricism and idealism, and argued for a view of universals as tropes. His influence swayed Oxford away from idealism and, through figures such as H. A. Prichard, Gilbert Ryle and J. L. Austin, his ideas were also to some extent at the origin of ‘moral intuitionism’ and ‘ordinary language philosophy’, which defined in turn much of Oxford philosophy until the second half of the twentieth century. Cook Wilson’s name was, however, all but forgotten by the end of the century, but the influence of his ideas is still felt today in the writings of philosophers as diverse as John McDowell, Charles Travis and Timothy Williamson.