Richard de Clare, 6th Earl of Gloucester

Richard de Clare inherited a vast empire of lands stretching from the Welsh Marches to East Anglia, making him one of the most formidable magnates in 13th-century England. As the 6th Earl of Gloucester, his primary power base was the volatile Welsh border, where he held the mighty Lordship of Glamorgan. His life was defined by the tense struggle between crown and aristocracy. Initially a supporter of King Henry III, he grew increasingly frustrated with the king's mismanagement and favoritism toward foreign courtiers. This discontent propelled him into the arms of the reformist barons led by Simon de Montfort. Richard became a key signatory of the Provisions of Oxford in 1258, which sought to curb royal power. His allegiance, however, was a stormy one; he later broke with de Montfort, only to be captured at the Battle of Lewes. His death in 1262, at the brink of all-out civil war, removed a pivotal and unpredictable figure, whose vast resources and Marcher lordship made him a kingmaker in a conflict that would reshape English governance.