This article discusses the genre of prehistoric science fiction and its exploration of notions of the genesis of religion and the identities of old gods and goddesses from 1880 to 1955. Beginning with an introduction to the contemporary anthropological context (Edward Tylor, James George Frazer, Sigmund Freud, Jane Harrison, and Margaret Murray and their speculations on deities from Mithra to Isis), it then discusses both obscure and canonical science fiction texts in this context, many of them little known or never before discussed in the context of theological history. Authors whose work is considered include Andrew Lang, H. G. Wells, Rudyard Kipling, Henry Rider Haggard, S. Fowler Wright, Henry Marriage Wallis, Naomi Mitchison, and William Golding. The article draws attention to the gendered implications of imagining ancient deities, with goddess fictions significantly more optimistic than those about gods: the shape of things to come in both the practice of modern pagan religion worldwide and the decline of Christian practice in Britain. Fictions of old gods emphasize pessimism, despair, and human fallibility and even sometimes conclude with outright atheism; fictions of old goddesses feature heroic and sympathetic protagonists and can offer a satisfying and harmonious alternative to Christianity. The earth, mother, and virgin goddesses who emerge from these fictions went on to shape both contemporary literature and contemporary and current religion. Indeed, one has even shaped modern science: William Golding’s goddess Oa, who inspired James Lovelock’s Gaia, symbol of the earth as a self-sustaining system. These apparently obscure and ephemeral texts thus show how fiction contributed to and shaped the religious politics of late Victorian and early twentieth-century Britain: as writers used fictional work to try out reinvented old deities for new times, pagan and broadly feminist goddesses triumphed over avatars of the Christian god in a prefiguring of trends in twentieth-century British spirituality.