The 1014 battle of Clontarf and the 1169–71 Anglo-Norman invasion were two defining moments of medieval Irish history. Clontarf in the popular consciousness marked an end to both the high-king of Ireland Brian Boru and Ireland’s Viking Age. Meanwhile, the Anglo-Normans originally arrived on Irish shores to support their ally, King Diarmait MacMurrough of Leinster, but MacMurrough has since been scapegoated as the man responsible for beginning the wider Anglo-Norman conquests of Ireland. These two figures remain highly controversial, but too much emphasis on them has overshadowed who and what came between, demoting the intermediate period to a ‘snappy epilogue or a lengthy prologue’. To correct this issue, it is imperative to utilise a ruler who not only arose in post-Clontarf Ireland but interacted with early Norman England, and that figure is the eleventh-century King Diarmait mac Maíl na mBó (c.1000–72).