(1312–33), earl of Ulster, called ‘the Brown Earl’ by Gaelic annalists. His assassination near Carrickfergus by some of his own knights speeded the disintegration of the lordships of Ulster and Connacht. William was the grandson and heir of Richard, the Red Earl; his mother was Elizabeth de Clare, an heiress of the earl of Gloucester. After his marriage to Edward III's cousin Matilda of Lancaster, he came to Ireland in 1328 and was embroiled in conflicts with the Ist earl of Desmond, the Mandevilles of Ulster, and his own kinsman Walter de Burgh, who dominated Connacht. While serving as king's lieutenant in 1331–2, he took strong action against his opponents, imprisoning Walter de Burgh in the castle of Northburgh, where he died. It was this that seems to have provoked the fatal conspiracy against him, as he was preparing to join Edward III on campaign in Scotland.
From The Oxford Companion to Irish History in Oxford Reference.
Subjects: European History.