Darius = "lord"

 1) Darius the Mede, the son of Ahasuerus, king of the Chaldeans, who
    succeeded to the Babylonian kingdom on the death of Belshazzar;
    probably the same as "Astyages" the last king of the Medes (538 BC)
 2) Darius, the son of Hystaspes, the founder of the Perso-Arian dynasty
    (521 BC)
 3) Darius II or Darius III
    3a) Darius II, Nothus (Ochus) was king of Persia during the time
        of Nehemiah (424/3 - 405/4 BC). Darius II is the most probable
        because he is mentioned by Nehemiah and ruled during the time
        of Nehemiah
    3b) Darius III, Codomannus was king of Persia during its last years
        at the time of Alexander the Great and was his opponent
        (336 - 330 BC)