a historic Anglo-Irish family associated with Connaught. Its founder was William de Burgo, of a knightly family from eastern England; he and his descendants were granted much of Connaught in the late 12th century, and his grandson Walter was also granted Ulster. Although Walter's great-grandson, William, left no male heir, his kinsmen succeeded in holding the bulk of the Burgh lands and, adopting Irish names, became virtually native chieftains. Their two main branches, those of “MacWilliam Iochtar” and “MacWilliam Uachtar,” acquired respectively the earldom of Clanricarde and the viscountcy of Mayo.