Who was Darius the Mede?

> And Darius the Mede received the kingdom, being about sixty-two years old. [Daniel 5:31] I have read much about the possible identities of Darius the Mede; to me, the most convincing alias is that of Gabaru (mentioned in Nabonidus Chronicle column iii line 20). However, there are a number of other theories, and it causes me to wonder: _Who exactly was Darius the Mede?_ I know we cant know for sure (?), but what would make the most sense, in light of our faith?