monarch

A monarch is a sovereign ruler of a state or territory. The term derives from the Greek monarkhos, meaning one ruler. In historical contexts, monarchs accumulated political authority through inheritance, conquest, and dynastic legitimacy.

Monarchies vary in power. In an absolute monarchy, the monarch holds ceremonial and executive authority with little or no constitutional constraint, as seen in some current states. In a constitutional or ceremonial monarchy, the monarch's duties are primarily symbolic, with real political power vested in elected representatives and an independent judiciary. Contemporary monarchies are often constitutional, and succession is typically hereditary, although modern reforms have introduced gender-neutral or elective succession in some regions.

Historically, monarchies were the primary form of governance across much of the world. The rise of constitutional frameworks and republican movements in the 18th–20th centuries reduced monarchs' political roles in many places, while still preserving ceremonial duties in many nations. Today, monarchs survive as heads of state in regions across Europe, Asia, Africa, and Oceania; examples include the United Kingdom, Sweden, Japan, Canada, and the Netherlands in constitutional roles, and Saudi Arabia or Brunei as more centralized. The monarch's influence often extends to cultural and ceremonial duties, diplomacy, and national identity.

In biology, the term monarch also refers to the monarch butterfly (Danaus plexippus), noted for its orange-and-black wings and long migrations. This use is unrelated to political rule but shares the common meaning of singular overall leadership or prominence in naming.