William I of Guelders and Jülich

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.

Mathilde quickly married John II, Count of Blois, and this grievance precipitated into the War of the Succession of Guelders.

At this time a marriage was arranged between the young William and Katherine of Bavaria, who had been betrothed to his uncle Edward.

He participated in crusades against the Lithuanians in East Prussia in the territories of the Teutonic Order with William of Holland, first in 1383, and later in 1388–89 and 1393.

His actions and alliance with England have been seen as reckless, and raised the ire of Charles VI of France, who advanced on Guelders with an army of 100,000.

The next year he made a pilgrimage to the Holy Land, and in the summer of 1391 he joined a French fleet to fight Moorish pirates of the coast of Barbary.

He returned to the crusades in Prussia in the winter of 1392 and 1393, and inherited the Duchy of Jülich (as William III) in 1393 upon the death of his father.

As part of his involvement in the Hundred Years' War, he played an important role as he was in control of the coronation road between Frankfurt and Aachen, which passed through his territory.

In the fall of 1401 William was intending to prepare to join his brother in law, John van Arkel, in his war against Duke Albert in Holland.

Had William lived longer, it is likely that he would have continued to resist Burgundian influence in the Netherlands, and his legacy was heavily tied with his external wars.

[1] Although these wars came at a cost for the people of Guelders and Jülich, his activity did allow for his counties to thrive economically and to unite against an external enemy.

Giesbert managed to work as a physician to Duchess Johanna and Antoine, Duke of Brabant, enemies of Guelders.

When sick in 1401 and 1402, other doctors were called: Derich Distel, Volpart, Evert vander Eze, and an English physician, Thomas.

In 1390 while visiting the King of England, he left Johann von der Velde called Honselaerr, who had fought with Duke William against Brabant in Grave.