John I of Montfort was a French nobleman born in 1294. He became the Duke of Brittany in 1341 after the death of his father, John III of Brittany. His claim to the duchy led to a conflict known as the War of the Breton Succession, where he faced rival factions, including the supporters of Charles of Blois. Throughout his life, John I struggled to maintain control over Brittany amidst political turmoil. He was known for his military leadership and efforts to secure his territory. John I died in 1345, leaving a legacy marked by the ongoing struggle for power in the region.