John III of Montfort was a nobleman from the 14th century, known for his role as the Duke of Brittany. He was born in 1339 and became the duke in 1341, following a disputed succession. His reign was marked by conflicts over the control of Brittany, particularly with rival factions and the French crown. John III's leadership was characterized by efforts to stabilize the region and assert his authority. He faced challenges from both internal and external forces, including the House of Blois. His tenure ended with his death in 1399, after which Brittany continued to navigate its complex political landscape.