John of Lancaster, 1st Duke of Bedford

Third son of Henry IV, brother to Henry V, John of Lancaster became regent of France in 1422 for his nephew Henry VI, then still a child. His military skill and administrative grip brought English power in France to its zenith, controlling vast swathes of territory through force and the critical alliance with Duke Philip of Burgundy. Then Joan of Arc arrived, and the momentum broke. Political quarrels at home drained support, funds dried up, and Burgundy wavered. The war ground into attrition. Bedford died on 14 September 1435 during the congress of Arras, just as Philip prepared to abandon England and make separate peace with Charles VII - the empire he'd built already collapsing beneath him.