A monarch is a ruler who rules because one of their relatives ruled. A male monarch is called a king, and a female is called a queen. Some monarchs are called emperors or empresses. It is a system of ruling, in which ruling starts off by a member of a family, and continues till the end of a family. Monarchs were very common in history. A lot of countries used to have a monarch, but no longer have them. They are now republics. Some countries that still have monarchs have other leaders that actually have the power. These are called constitutional monarchies.