Leo III was a Byzantine Emperor who ruled from 717 to 741 AD. He is best known for his military successes against the Arabs, particularly during the siege of Constantinople in 717-718, which helped to secure the empire's borders. Leo III is also recognized for initiating the Iconoclast Controversy, a significant religious dispute regarding the use of religious images in worship. Leo III implemented various administrative reforms to strengthen the empire and improve its economy. He reorganized the military and introduced the theme system, which divided the empire into districts governed by military leaders. His reign marked a pivotal period in Byzantine history, influencing both politics and religion.