William I of Guelders and Jülich
Duke of Guelders, as William I, from 1377 and Duke of Jülich, as William III, from 1393.
William was known for his military activities, participating in the Prussian crusade five times and battling with neighbors in France and Brabant throughout his rule. His allies included Holy Roman Emperors, Charles IV and Wenceslaus, Richard II of England, and Conrad Zöllner von Rothenstein, the Grand Master of the Teutonic Knights. During his reign the duchies of Guelders and Jülich were temporarily unified