Daniel was first — Belshazzar's promise to Daniel was, that he should be the third ruler in the kingdom, Daniel 5:7, Daniel 5:16, Daniel 5:29. The first was general of the army, the second president of the palace, the third of the land and provinces.
Related Commentaries of Daniel 6:2
Daniel 6:2
2 And over these three presidents; of whom Daniel was first: that the princes might give accounts unto them, and the king should have no damage.