Darius: Dan 1:21, Dan 5:31, Dan 6:1, Dan 6:28, Dan 11:1
Ahasuerus: This was the Astyages of the heathen historians; as we learn from Tobit 14:15, where the taking of Nineveh is ascribed to Nebuchadnezzar and Assuerus, who were the same with Nabopolassar and Astyages.