Who can resist the allure of Merlin? In British and Celtic mythology, Merlinus Ambrosius is perhaps the most compelling of the many charismatic figures associated with King Arthur and the Grail. For 1500 years the great enchanter has ensnared legions of willing interpreters in his web of powerful charms and spells. In her ebullient new history, one of Britain's foremost authorities on Welsh and Celtic folklore traces the 'birth' of Merlin in the writings of Geoffrey of Monmouth to the rise of the wise royal counsellor in Sir Thomas Malory; disentangles the benign, donnish Merlin who lives time backwards in T H White's The Once and Future King from the dangerous, atavistic Merlin of C S Lewis' novel That Hideous Strength; and transports her readers to Merlin's multiple settings in Wales (from mythic Carmarthen to a towering, windswept Cader Idris). Richly illuminating both historical sources and intertwined strands of legend and myth, the author shows that, whether in literature, art, TV or cinema, this primeval mage and sorcerer has been a constant, mesmerising presence in the foundation stories of the British Isles.