Undertaking a biography of Henry III is a challenge for the simple fact that he reigned for 56 years. Indeed, it’s possible to find articles about him where whole decades of his rule are missing. The last full-scale attempt at a biography resulted in Maurice Powicke’s King Henry III and the Lord Edward in 1947. His work deserves its legendary status, but it is more thematic than chronological, more analysis than narrative, and this can pose a problem for people new to the era. Most of the modern work on Henry has been independent studies or as part of biographies of his contemporaries. The Henry in my own biography of Simon de Montfort, the first edition anyway, is the portrait devised by Victorian and Edwardian scholars, a nice family man who was simply not up to the rigours of kingship. Even as it was released, I had the feeling that something was missing. A weak and inept king for so long, in an era of such great changes happening in politics, justice, education and the arts, didn’t make much sense. So I set about writing a chronological life of the king. But old habits die hard, so as I entered each new decade of his reign, I said to myself, ‘Now we’ll see the Henry we all know’. And yet, like that, I was on his deathbed and convinced he was the greatest king of England who ever lived. This is his story here.