Darius the Mede

There is a lot of discussion among commentators about Darius the Mede, introduced in Daniel 5:31 when he took over the kingdom of Babylon from Belshazzar, because there is no record of him outside the Bible. As the editor of The Daily Bible commented on the September 21 reading, many think this was a man named Gubaru who was put in charge of Babylon by the Medo-Persian king Cyrus. There are a couple reasons this is the most likely possibility according to the Archaeological Study Bible (p.1396):

1. Daniel 9:1 states that Darius was made king.
2. The book of Daniel never refers to him as the king of either Persia or of the Medes but simply as the ruler of Babylon.

Gurbaru is actually mentioned in Babylonian inscriptions as the governor that Cyrus put in charge of the newly conquered Babylonian territories (Concordia Self-Study Bible).

From what I've read, it sounds like comments by The Daily Bible editor at the end of today's reading about Darius "betraying his own nation" to Cyrus are inaccurate since Darius was working on behalf of Cyrus all along.