Below is the evidence that supports that Darius the Mede was in fact Darius I before he became king of Persia:
|Darius the Mede||Darius I|
|Received the kingdom of Babylon (Daniel 5:31), apparently from Cyrus II, making him a vassal king.||Cyrus II was not called "King of Babylon", but Darius I was. The Babylonians revolted against him after he became the sovereign ruler of Persia.|
|May be Gubaru, (Gobryas or Ugbaru) Cyrus II's Midian general whom he invaded Babylon with and is said to have appointed as governor of Babylon, during which it would seem he took the name Darius.||Was a commander under Cyrus II whom Cyrus feared would attempt a coup. Who would he fear more than the one who helped him conquer the previous world power? Being appointed as a governor while calling himself king of Babylon would be further good reason for this fear. There was no military record of Darius before his Persian kingship.|
|Called "The Mede" and a "descendant of the Medes" (Daniel 5:31; 9:1)||Overthrew Gaumata with the claim that he was a Magi Mede imposter, but no proof was ever presented. He perhaps made the claim to draw attention away from his own origins as such.|
|Proceeded to go through many pains to prove that he himself was a Persian descendant of Achaemenid with a genealogy that was never verified and was contradicted by other genealogies of which he declared them false genealogies.|
|Set up the center of his kingdom at Ecbatana of the Medes.|
|Worshiped Ahuru Mazda, the god of the Zorastrians, which started out as the Midian religion, not Persian.|
|Set up 120 Satraps over the territory of the former Babylonian kingdom. (Daniel 6:1) In a cuneiform tablet, Gubaru is said to have appointed sub-governors over Babylon.||Was noted for his reorganizing the Persian empire into a system of Satraps over provinces along with many other ground-breaking reforms.|
Give this some thought. The question I've asked myself is why the critics refuse this explanation. The answer is simple: If Darius the Mede is proven to be a historical figure, just as Belshazzar was proven to be, then that would provide strong evidence that Danial was in fact a true prophet in the days of the Persians, as much of what he prophesied were proven to come true much, much later in the time of the Greeks and Romans.
But who was Ahasuerus, whom Daniel says Darius I was the son of? According to Jewish historical sources, it was Cyaxares, (uncle and father in Law of Cyrus II,) who appears in Darius I's own publicized genealogy, known as the Behistun Inscription. Greek sources recognize Cyaxares as well, though some feel his placement in the Achaemenid line to be dubious, or at best an error of placement, in line with the above information, believing "Cyaxares" became a family head name or was switched, as a scribal error in the Behistun Inscription. Though this is not to say that he had no Persian blood at all, but that he in fact did have Midian blood. Note that "Xerxes" may be a shortened form of "Cyaxares". "Xerxes" being the Greek pronunciation of Ahasuerus.
And think about this: What is the likelihood that two rulers in the same government would share the same name at the same time that has never once appeared in the history of its rulerships before that time?
These things may be seen as confirmation bias, but is it? Confirmation bias requires ignoring facts that contradict, but there are no facts that contradict this except documents that contradict each other. When two or more documents contradict each other, only one of the documents can be chosen as truth. Those of us who view the Bible as God's word will focus on the Bible as the source of immutable facts, therefore all other facts that contradict each other must be chosen based upon their support of the Bible account. Historians are regular users of confirmation bias in taking every effort to disprove the Bible account without justification and with no evidence to support their conclusions, only verbal acrobatics that they design to contradict the Bible. When you look at just the facts, though, the Bible's account stands out and makes the true story stand out.
Darius the Mede
Ahasuerus (Book of Daniel)
Cyrus the Great
Gobryas (Cyrus the Great's general)