Rulers

Ruler is a term with two main meanings: a person who exercises supreme authority in a polity; and a tool used to measure or draw straight lines. In the political sense, rulers range from monarchs and dictators to presidents and elected leaders. Their formal powers, legitimacy, and methods of succession vary by system and era.

In history, rulers have claimed sovereignty through heredity, conquest, appointment, or popular mandate. Some states have fused or separated heads of state and government. The development of constitutional rule and the rule of law has limited or balanced royal or autocratic authority in many regions, while others retained centralized authority into the modern era.

Ruler (tool) is a straightedge used in geometry, drafting, and construction to mark and draw straight lines or measure lengths. Common forms are flat bars of wood, plastic, or metal with markings. Metric rulers typically show centimeters and millimeters, while imperial rulers may show inches divided into fractions. Specialized rulers include combination scales and engineers' rulers.

Construction and use: rulers require a stable edge and flat surface; accuracy can be affected by warping, wear, or improper alignment. In design and manufacturing, rulers underpin precise measurement, layout, and alignment; often paired with calipers, protractors, and squares.

Rulership and rulers as instruments intersect with culture, law, and technology, reflecting how societies organize power and measure space.