William I, Elector of Hesse (or Hesse-Cassel), also known as William IX, Landgrave of Hesse-Kassel, (1743–1821)
William was excommunicated a second time for "abducting" the Viscountess Dangerose (Dangerosa), the wife of his vassal Aimery I de Rochefoucauld, Viscount of Châtellerault.
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She was also mistress to her granddaughters' paternal grandfather William IX, Duke of Aquitaine.
Schlieffen became the most important adviser of Landgraves Frederick II and William IX.
Ida joined the Crusade of 1101: alongside Thiemo of Salzburg and the dukes Welf IV of Bavaria and William IX of Bavaria, she raised and led her own army toward Jerusalem.