(1) A king described as "Darius the Median," who "took the kingdom," being then about 62 years old, on the night in which Belshazzar, the king of the Chaldeans was slain (Dan. v. 30, 31).
    (2) A "king of Persia" who in point of time followed after Cyrus (Ezra iv. 5).  When he came to the throne, the building of the Temple had been suspended owing to complaints from the jealous neighbouring tribes; but Darius, on being applied to, caused a search to be made at Achmetha (Ecbatana), the Median capital, where the edict of Cyrus permitting the work to be undertaken was found (Ezra vi. 1-12). (The Sunday School Teacher's Bible Manual, Hunter, 1894)

Dar (to possess) is the root of Dareyavesh, called by Greeks Δαρειος; by Romans, Darius; by Ferdosi, Dareb—the title whence the gold coins of Persia were known to the Greeks as daries.  There is reason to suppose that Darya-oush (Dareyavesh) was rather a royal prefix than a proper name; since him whom the Greeks knew as Darius Nothus, or the bastard, is the first Dareb of the Shah-nameh.  The Darius of Daniel is the Greek Cyaxares the Mede, the Kai Khaoos of Ferdosi, the old Persian Uvakshatara (beautiful eyed).  The Darius of Ezra, the Darius Hystaspes of the Greeks, is in the Shah-nameh Gushtasp; in old Persian, Vishtaspa (possessor of horses), a curious coincidence with Herodotus' story of the manner in which he was raised to the throne, as well as with the legend that his horse's legs were drawn up into its body and were released by a miracle of Zoroaster.  Gushtasp is, however, by some, thought to have been the father of Darius, the Hystaspes of the Greeks, and, perhaps, true heir to the throne; but who waived his right in favour of his son, lived and served under him, and, finally, was killed by the breaking of the rope by which he was being let down to inspect the sculptures of the monument that Darius was preparing in his own life-time. (History of Christian Names, Yonge, 1884).