Kepler,
the Darius in Daniel is said to have received the kingdom over the Chaldeans, which shows that he was given it, obviously by Cyrus. After his short reign over the districts of Babylon he died, and according to the numerous cuneiform contract tablets, Cyrus assumed the title King of Babylon in addition to King of Lands not before towards the end of his first year (after the accession year). The rulership over Babylon had been given to a certain Ugbaru, who with much probabability is identical with Darius (the Mede) of Daniel.
Furthermore, Ezekiel refers to Daniel, in order to support his authority, which certainly was questioned by many due to his "collaboration" with the Babylonian Empire that had destroyed God's Temple and the Holy City. The later (fable and fairy tale type) additions to Daniel indicate (in addition to the strong internal evidence) that the original portion was quite a good bit older.
I personally cannot think of many books that impressed me greater than this of Daniel. And not so much because of the detailed prophecies, but because of the great vision and the impressive personality of this important man, who seemed to have been rightly honoured so much by God and men.
The Writiings of the Apostles and Disciples would somehow hang in the air, if Daniel were not the person I perceive him to have been. They would have all been wrong.
More wrong can be found with the critics. They know little - it is very ancient material we are dealing with - but assume much. Their ridicule is more telling then their insistance on absent evidence.