Duke of Normandy as the reign of William II (1035–87), the ruler of Normandy could style himself "prince and duke, count of Normandy" as if unsure what his title should be. The literal Latin equivalent of "Duke of Normandy", "dux Normanniae", was in use by 1066, but it did not supplant "dux Normannorum" until the Angevin period (1144–1204), at a time when Norman identity was fading. Richard I experimented with the title "marquis" ("marchio") as early as 966, when it was also used in a diploma of King Lothair. Richard II occasionally used it, but he seems to have preferred the title duke.
John IV, Duke of Brittany John IV, Duke of Brittany John IV the Conqueror KG (in Breton Yann IV, in French Jean IV, and traditionally in English sources both John of Montfort and John V) (1339 – 1 November 1399) was Duke of Brittany and Count of Montfort from 1345 until his death and 7th Earl of Richmond from 1372 until his death. He was the son of John of Montfort and Joanna of Flanders. His father claimed the title Duke of Brittany, but was largely unable to enforce his claim for more than a brief period. Because his father's claim to the title was