An individual who has been granted a large area of land and given a distinct title indicate their being important and belonging/owing allegiance to a kingdom or realm. Such individuals are above Barons in most systems, their land usually being made up of Baronies and other lands that may be held by rich merchants or simply unowned.
The highest title of nobility in England, ranking below the prince, introduced for the first time by Edward III when bestowing various castles and estates in Cornwall to his son, the Black Prince. The title, imported from the continent, originally meant a military commander, and the English retained this etymology by endowing English dukes with special fees in war, where command expertise was expected. In Germany, the title ‘Herzog' was equivalent, though they were often elected and carried more administrative and social duties than military ones. A duke is properly addressed as ‘ your grace', equivalent to the rank of archbishop in the church hierarchy. Within the SCA the title is reserved for those gentles who have served twice as king of an SCA kingdom, won through the Crown Tournament. They are know by coronets bearing strawberry leaves in the familiar three leaf patterm, ranking just below the Princes of the realm.