John IV, Duke of Brittany was a prominent nobleman in the late 14th century, born around 1389. He became Duke of Brittany in 1399 and was known for his efforts to maintain the independence of Brittany during a time of political turmoil in France. His reign was marked by conflicts with the French crown and internal struggles within Brittany. John IV was a supporter of the House of Montfort, which played a significant role in the history of Brittany. He was involved in the Brittany Civil War, which pitted the Montforts against the House of Blois. His leadership helped solidify the Montfort claim to the duchy and contributed to the region's unique identity.