Ronald Dworkin, who has died aged 81, was widely respected as the most original and powerful philosopher of law in the English-speaking world. In his books, his articles and his teaching, in London and New York, he developed a powerful, scholarly exegesis of the law, and expounded issues of burning topicality and public concern – including how the law should deal with race, abortion, euthanasia and equality – in ways that were accessible to lay readers. His legal arguments were subtly presented applications to specific problems of a classic liberal philosophy which, in turn, was grounded in his belief that law must take its authority from what ordinary people would recognise as moral virtue. Dworkin studied philosophy (under Willard Van Orman Quine at Harvard University and, informally, with JL Austin at Oxford University) and law at both Oxford and the Harvard Law School. He worked as clerk to the great US judge and legal scholar Billings Learned Hand and as a practising associate in the Wall Street law firm Sullivan & Cromwell, before teaching law at the Yale and later the New York University law schools, as well as at Oxford and later University College London. This broad education and training, sharpening the analytical skills of a quite exceptionally powerful intellect, enabled him, even as a precocious young man, to challenge the most eminent figures in the world of law and jurisprudence, including Hand and HLA Hart, the renowned exponent of legal positivism – considering the social basis of a law separately from its merits – at Oxford. Perhaps Dworkin's greatest achievement was his insistence on a rights-based theory of law, expounded in his first and most influential book, Taking Rights Seriously (1977), in which he proposed an alternative both to Hart's outlook and to the newly minted theories of the Harvard philosopher of law John Rawls.