John William, Duke of Jülich-Cleves-Berg

Johann Wilhelm of Jülich-Cleves-Berg (German: Johann Wilhelm, Herzog zu Kleve, Jülich und Berg) (28 May 1562 – 25 March 1609) was a Duke of Jülich-Cleves-Berg.

His parents were William the Rich, Duke of Jülich-Cleves-Berg (1516–92) and Maria of Austria (1531–81), a daughter of Ferdinand I, Holy Roman Emperor and Anna of Bohemia and Hungary. He grew up and was educated in Xanten. Johann Wilhelm became Bishop of Münster. However, after the unexpected death of his elder brother Karl Friedrich, Wilhelm was needed to succeed his father as Duke of Jülich-Cleves-Berg, a secular fief. He was also Count of Altena. The United Duchies of Jülich-Cleves-Berg was a combination of reichsfrei states within the Holy Roman Empire.

Johann Wilhelm was first married in 1585 to Jakobea of Baden (d. 1597), daughter of Philibert, Margrave of Baden. He was secondly married to Antonia of Lorraine (d. 1610), daughter of Charles III, Duke of Lorraine.

He was subject to mental illness, for which he was treated by the physician Francesco Maria Guazzo.

Upon Duke Johann William's death in 1609, his inheritance was claimed by the heirs of his two eldest sisters: the heir of Maria Eleonora of Cleves (1550–1608), the eldest sister and married to Albert Frederick, Duke of Prussia, was Anna of Prussia, the Electress of Brandenburg, a Protestant. The second sister was Anna of Cleves (1552–1632), married with Philipp Ludwig, Count Palatine of Neuburg, and her son and heir was the then Count Palatine of Neuburg, a Catholic.

The disputes of the epoch between Protestants and Catholics escalated, leading to the Thirty Years' War in 1618; the succession dispute became part of the war. Ultimately, Brandenburg received Cleves-Mark and Neuburg received Jülich-Berg, after the lands had been trampled under military several times and lost much of the fabled wealth so renowned in Duke Wilhelm's time. Among his court servants and employees were the composer Konrad Hagius.