Darius I was a crucial king of the Persian Empire who reigned from 522 BCE to 486 BCE. He consolidated his rule by putting down rebellions across the empire after gaining power. Darius then expanded the empire through military campaigns, establishing 20 provinces and incorporating new lands like Egypt and the Indus Valley. He also reformed the government system and introduced a new universal currency. Darius was succeeded by his son Xerxes I after his death in 486 BCE.