Royal

A Royal is a member of a kingdom's ruling family. The title is generally hereditary or acquired by marriage; however, rulers and ruling families can change in less common ways as well, such as via hostile takeovers or the retraction of the previous ruling family. The royal family, or "monarchy", can consist of a King patriarch, a Queen matriarch, and Prince and/or Princess heir(s).

Royalty in One Piece
Most kingdoms in the world of One Piece are ruled by a royal family of some sort. Most of the rulers are monarchs, but they can go by a variety of names and titles: for example, "Empress" in Amazon Lily, "God" in Skypiea, "Duke" or "Master" in Zou, and "Shogun" in Wano Country. The patriarch of the Kamabakka Kingdom is referred to as "Queen" due to the culture of the kingdom.

The titles can be revoked with the replacement of the ruler by means of force, rebellion of the people, the monarchy abandoning their kingdoms, or by the the members of the royal family. Rulers who have abandoned their kingdoms and their descendants may reclaim the country's throne at any point.

Royal Guards
Some kingdoms have Royal Guards, organizations given the job of guard the royal family. The total responsibility of these organizations vary from nation to nation, from simply standing guard and protecting internal areas to functioning as the main fighting force of their kingdom.

World Nobles
World Nobles, also known as Celestial Dragons, are the descendants of the First Twenty, the royalty who took down the Great Kingdom and founded the World Government 800 years ago. As the descendants of the World Government's founders, the World Nobles have ultimate authority, and are permitted to commit any crimes, even to other members of royalty.

Unlike royalty of individual nations, World Nobles are always under the protection of the Marines, and they have the authority to summon a Marine Admiral.

Levely
The Levely is a council of 50 of the monarchs of World Government nations. Every four years, these monarchs meet in Mary Geoise to discuss various issues of international importance. During this event, the visiting royalty are treated equally without regard for their home country; however, they are still subject to the whims of the World Nobles.