One of the counties in each duchy is the capital and is normally held by the duke of that duchy. If that county's capital is a city or temple then the realm is a republic or theocracy respectively. Kingdoms and empires can also be republics and theocracies if the capital of the realm is a city or temple.
For most cultures, the ruler of a duchy is a duke (male) or duchess (female), but there are several exceptions:
- Doux/Duchess (Greek)
- Emir/Emira (Arabic, Iranian)
- Beylerbey/Beylerbayan (Turkish)
- High Chief/High Chief (Mongol)
- High Chief/Duchess (Pagan)
- Jarl/Duchess (Norse Pagan)
- Farbas/Farba (West African)
- Grand Prince/Grand Princess (Russian)
- Huecalpixqui/Huecalpixqui (Nahua)
Note religous title variants 'trump' cultural ones. For example, a duke with Mongol culture and Tengri pagan religion will be known as a High Chief.
Similarly, duchies themselves can also be known by other names:
- Emirate (Arabic, Iranian, West African)
- Beylerbeylik (Turkish)
- High Chiefdom (Mongol)
- Grand Principality (Russian)
The titles of duchies and dukes in republics and theocracies are different still.