The Sovereignty is another term for royalty, and each country has one. The tradition is only followed by humans; elves and dwarves do not follow the rules or worship of the Sovereign. It is divided into a hierarchy of power and influence:
Royal rank is not titled as per gender. There is one sole ruler at a time, known as the Sovereign. They are the immediate son or daughter of the former Sovereign and Regent. The line to the throne goes from oldest to youngest. Siblings of the present Sovereign move down the line if the current Sovereign bears children. The more children they have, the further down the line they go.
As a result, it is not unusual for a Sovereign to only bear one or two children.
The Sovereign is the ruler of Olvian, and although many smaller tasks are delegated to The Regent, or minor lords and ladies, the Sovereign remains able at all times to overrule any law they see fit.
The Regent is the husband or wife of The Sovereign. Marriages are not always arranged, but the Regent must be of noble birth, and usually resides in another country. This not only helps international relations, but also ensures that no local nobles try their hand at usurping.
Whilst sexuality is not frowned upon generally in Olvian, the Regent and Sovereign must be biologically able to birth an heir. Therefore it's very common for both the Regent and Sovereign to have a mistress or a mister - a person with whom they can pursue a casual relationship. Any resulting children have no claim to power or the throne.
The only time a Regent is promoted to power is if there are no children. However, since it is seen as 'soiling' the bloodline to allow a Regent on the throne, it is imperative that the royal family have at least one child, but it is seen as 'confusing things' to have more than two.
Throne Advisers are the surviving parent Regent of the present Sovereign. As a Regent cannot lay claim to the throne, on the death of the current Sovereign, they are automatically promoted to role of Throne Adviser to the newly appointed Sovereign.
If no parents survive, then a Throne Adviser can be appointed by the Sovereign directly - providing he or she chooses to have one.