John IV, Duke of Oldenburg was a German nobleman who ruled from 1573 until his death in 1603. He was a member of the House of Oldenburg, a prominent dynasty in northern Europe. John IV is known for his efforts to strengthen the duchy and promote economic development during his reign. He was also involved in the political dynamics of the region, navigating relationships with neighboring territories. His rule contributed to the stability of Oldenburg, and he is remembered for his commitment to the welfare of his subjects and the advancement of his duchy.