Rollo the founder of Viking Normandy was almost certainly not Duke of Normandy and was most likely simply Count of Rouen. The same is probably true of his son William Longsword; whether it was the first or second Richard that first acquired the title Duke is uncertain.
Note that;
- sometimes Rollo is given as 'Robert I', with the subsequent Roberts renumbered
-William Longsword is similarly sometimes referred to as 'William I', and William the Bastard as 'William II'
William the Bastard famously became king of England in 1066 after the battle of Hastings in 1066. On William's death in 1087, the succession was split; son William Rufus became king of England whereas son Robert became Duke of Normandy and held it until brother Henry took it from him in 1106.
Subsequently Normandy passed to Stephen as ruler of England. Control passed briefly to Matilda the Empress, before coming back to Stephen until Matilda's husband Geoffrey of Anjou gained Normandy in 1144 and passed the duchy onto his son Henry in 1150 who subsequently became king of England in 1154.
King John lost control of Normandy to the French king, Philip Augustus in 1204, a loss that was confirmed by his defeat at the battle of Bouvines in 1214. Later kings such as Edward III, Henry V and Henry VI had varying degrees of success in recovering Normandy and other French possessions of the English crown, but were ultimately not successful.
But despite losing control of Normandy itself the title Duke of Normandy remained in the possession of the English crown. Technically speaking Elizabeth II, the current queen of England is still Duke of Normandy, although the title itself is only used in reference to the one surviving piece of the old Duchy of Normandy that owes allegiance to the crown of England, namely the Channel Islands, who drink their loyal toast to 'The Duke of Normandy, our Queen'
.
Counts of Rouen and Dukes of Normandy
For subsequent Dukes see Rulers of England