Duke John IV of Saxe-Lauenburg was a German nobleman who ruled from 1422 until his death in 1425. He belonged to the House of Ascania and was the son of Duke Eric I. His reign was marked by efforts to strengthen his duchy and maintain its independence during a time of political instability in the region. John IV's rule was relatively short, but he is remembered for his attempts to navigate the complex relationships between various German principalities. After his death, the duchy was inherited by his brother, Duke Eric II, who continued the family's legacy in Saxe-Lauenburg.