Answer: D. King of Kings
Darius was the fourth king of the Persian Achaemenid Empire. Darius is one of the most famous Persian kings, as he ruled the empire at its peak. Although the king met with rebellions several times, he was able to control them every time. Darius was responsible for implementing Aramaic as the official language of the empire, and for developing a new monetary system. He also contributed to the centralization and unification of the empire.