Richard I, also known as Richard the Fearless, was the count of Rouen from 942 to 996. Dudo of Saint-Quentin, whom Richard commissioned to write the "De moribus et actis primorum Normanniae ducum", called him a dux. However, this use of the word may have been in the context of Richard's renowned leadership in war, and not as a reference to a title of nobility. Richard either introduced feudalism into Normandy or he greatly expanded it. By the end of his reign, the most important Norman landholders held their lands in feudal tenure.

In the Middle Ages, the duke of Normandy was the ruler of the Duchy of Normandy in north-western France. The duchy arose out of a grant of land to the Viking leader Rollo by the French king Charles the Simple in 911. In 924 and again in 933, Normandy was expanded by royal grant. Rollo's male-line descendants continued to rule it until 1135, and cognatic descendants ruled it until 1204. In 1202 the French king Philip II declared Normandy a forfeited fief and by 1204 his army had conquered it. It remained a French royal province thereafter, still called the Duchy of Normandy, but only occasionally granted to a duke of the royal house as an appanage.