Merlin, who became King Arthur’s magician, is one of the strongest figures in legend and literature. Ancient tradition portrays him in a mysterious environment of dragons and demons, Celtic enchantment and pre-Celtic megaliths, early Christianity and ancient druidry. Was there only one Merlin, or were there several? Was he mortal or not? Why can he still fascinate writers of science fiction? Geoffery Ashe considers all these matters.