Arthur I, Duke of Brittany was born in 1187 and became the Duke of Brittany in 1196. He was the son of Geoffrey Plantagenet, the Duke of Brittany, and Constance of Brittany. Arthur was a key figure in the power struggles of medieval France and England, particularly during the reign of his uncle, King John of England. Arthur's claim to the English throne made him a rival to King John, leading to conflict. In 1203, he was captured by John and later disappeared under mysterious circumstances, likely murdered. His death had significant implications for the political landscape of Brittany and the broader region.