What Persian ruler established the largest empire known?

Cyrus the Great established the largest empire known in the ancient world, founding the Achaemenid Empire in the 6th century BCE. His conquests expanded Persian territory across three continents, including parts of Asia, Europe, and Africa. Cyrus is renowned for his innovative governance, respect for local customs, and the creation of the Cyrus Cylinder, which is often considered the first charter of human rights. His legacy set the foundation for subsequent Persian rulers and the vast empire that followed.