American Protestant theologian, Harvard Divinity School professor for most of his career, and one of the most publicly engaged American theologians of his generation. Cox's The Secular City (1965) was a surprise international bestseller — more than a million copies in ten languages — that crystallized a moment in postwar Protestant thought. Against an older lament that modern urban secularization was the enemy of faith, Cox argued that the secular city was itself a legitimate outworking of biblical themes: the disenchantment of nature, the desacralization of politics, and the relativization of all inherited values are already at work in Exodus and the prophets. Christianity, he thought, should stop mourning the old sacral order and learn to do theology from within the new one.
His subsequent career tracked the actual religious dynamics of the late 20th century more honestly than The Secular City's thesis would have predicted. Turning East (1977) documented the Western encounter with Asian religious traditions. Fire from Heaven (1995) took global Pentecostalism seriously as the most rapidly growing form of Christianity on earth — a phenomenon the "secular city" thesis had not seen coming. The Future of Faith (2009) argued that religious life in the 21st century is moving past both the Age of Belief (doctrinal orthodoxy) and the Age of Faith (institutional Christianity) into an Age of the Spirit characterized by experiential, pluralist, and action-oriented religion.
Cox marched in Selma, worked on the 1960s World Council of Churches, and taught generations of divinity students. His posture throughout was that of a theologian who reads newspapers — committed to taking the actual religious life of actual people, wherever and however strange, as theology's proper subject.