A.J. Mackenzie is the pseudonym of Marilyn Livingstone and Morgen Witzel, an Anglo-Canadian husband-and-wife team of writers and historians. They write non-fiction history and management books under their own names, but 'become' A.J. MacKenzie when writing fiction. Morgen has an MA in renaissance diplomacy from the University of Victoria, but since the late 1990s has concentrated on writing books on leadership and management. Several of his books have been international best-sellers. Marilyn has a PhD in medieval economic history from the Queen's University, Belfast. She is a musician who writes music and also plays in a silver band and sings in an a capella trio. They have written two books of medieval history together, and also several novels, including the Hardcastle & Chaytor mysteries set on Romney Marsh during the French Revolution.