Duke/Duchess

Spouse: Duke or Duchess   Children: the Heir - typically the firstborn - is a Count/Countess if the duchy capital is landlocked, or a Marquis if the capital is coastal. Other remaining children are Lord or Lady

Requirements

Typically a Duke is a hereditary title, with the oldest child eligible to take up duties once they've reached the age of majority. Often they will spend their late teens and early 20s living in the capital, shadowing local levels of government and learning the laws and customs of their people. If they show an intent in being a Duke or Duchess, they will also participate in military service in this time rame. Unlike lower nobility titles, the child of a Duke cannot take the title until they are crowned as such.   If a Duke or Duchess leads troops into conflict, they may choose one of their Knights instead of their children to be their successor if the Knight showed exemplary leadership in combat. A ruling Monarch may also bequeath the title of Duke to a knight and give them land if a country expands or if an entire family line ends.

Duties

Ruler of a Duchy / State, Either gender can be awarded the title and are equal in ruling

Responsibilities

Dukes and Duchess are tasked with the management of a duchy or province - if there are no upper nobles assigned to it. a Prince or Princess may marry into a province and elevate their a high rank, but they also may just as well oust the ruling Duke and replace them. Dukes are responsible for working with the Barons or Baronesses that govern the cities in their land, and the Marquis, Margrave, Count or Countess that see to the counties. They need to make sure these groups of civilians live in harmony with each other, and that the needs of all are met.   Most Dukes and Duchesses are military trained, and may be called into leading troops in conflicts. Is is not unheard of for the knights that serve under a Duke or Duchess to be elevated to successor if they showed exemplary leadership in combat
Dukes and Duchess are responsible for enforcing the laws of the land, as given to them by the royal family, but in turn, are the voice of the people to the crown.

Accoutrements & Equipment

A duke or duchess is entitled to wear a coronet if they so desire. In the Eastern Gates Empire is still a common practice, while in the West Archway Kingdom it is typically only worn for the most formalist of occasions - state funerals, royal weddings, or coronations.

Grounds for Removal/Dismissal

Duke and Duchess are lifetime positions, that is held until one's death. While rare, a Duke may wish to hand responsibility over to their adult children, or a chosen knight and retire. This is usually after the Duke and Duchess are both over 70, and again, is quite rare.
A living but retired Duke would be called a Duke Emeritus. A living but retired Duchess would be called a Duchess Dowager
The Royal family could also replace a Duke or Duchess as they see fit if they feel the family is not upholding their duties. They must be careful in doing so, because of they don't have the support of the citizens and of the military, their replacements may be rejected. Often with violence.
Type
Nobility, Hereditary
Form of Address
Your Grace
Alternative Naming
Duke, Duchess
Length of Term
life
Past Holders
Reports directly to
Prince/Princess