John Sadler was born and bred in Northumberland and he has worked for most of his career in the law. He previously managed the Heritage Centre for North Tynedale, and the Royal Fleet Auxiliary Association, now working as Heritage Officer for Durham County Council and lectures at the University of Sunderland Centre for Lifelong Learning. He also works as a battlefield tour guide, conducting parties of students, veterans and serving members of HM armed forces around the battlefields of the Western Front. He is an expert on medieval warfare and a prolific writer on the subject. He has made a particular study of the history of conflict between England and Scotland. His many books include Battle for Northumbria, Scottish Battles, War in the North 1461-1464, Border Fury: The Three Hundred Years War, Clan Donald's Greatest Defeat: The Battle of Harlaw 1411, Flodden 1513, The Battle for Crete 1941, Culloden 1746 and Bannockburn.