Duke John of Schleswig (c. 1450–1513) was a nobleman from the House of Oldenburg, a prominent family in Northern Europe. He served as the Duke of Schleswig and was known for his efforts to strengthen the duchy during his reign. His rule was marked by political challenges and conflicts with neighboring territories. John was also involved in the broader power struggles of the time, particularly with the Kingdom of Denmark. His lineage connected him to various royal families, influencing alliances and territorial disputes in the region. His legacy is tied to the complex history of Scandinavia during the late Middle Ages.