Heraclius was a Byzantine Emperor who ruled from 610 to 641 AD. He is best known for his military campaigns against the Persian Empire and the early Islamic conquests. Heraclius reformed the Byzantine military and administration, which helped strengthen the empire during a time of crisis. Heraclius is also notable for introducing the term "Roman" to refer to the Byzantine Empire, emphasizing its continuation of the ancient Roman Empire. His reign marked significant changes, including the use of Greek as the official language, which shifted the cultural identity of the empire.