Ashurbanipal (reigned 668-627 BC) was known to the Greeks as Sardanapalus and in the Old Testament as Asnapper Ezra 4, 10; Jastrow 1915, pg. 21. Ashurbanipal is best remembered for his library of Assyro-Babylonian literature. This library has yielded most modern knowledge of Mesopotamian tradition. His artistic side is also shown in his dedication to completing Sennacherib's construction projects, making it difficult to discern works from Sennacherib or Ashurbanipal. Militaristically, Ashurbanipal was forced to withdraw from Egypt (in ~660 BC) and then entered a very bloody long-term struggle against the Babylonians. The Babylonians were ruled by his own brother, and supported by the Elamites. He was fixated on the Elamites, trying diplomacy; raising children captives; and even beckoning for a king's held to be swiftly delivered to be hung in his garden.
The costly Elamite wars ended in 646 BC when Assurbanipal defeated Susa, a victorious culmination of his obsession with eliminating the Elamites. His reliefs reveal that he had even flayed an Elamite king, then took his severed head home so that he could admire it hanging on a tree in his garden while he relaxed with his queen under a grape arbor. However, his win was bittersweet because Assurbanipal had focused so many resources on controlling a truly hopeless region. The Assyrian government suffered and was plagued by internal strife.
Removing the Elamites allowed the Medes and Babylonians to rise; also, the Persians were beginning their encroachment. Assyrian control over the far west of Egypt and the Levant fell apart, the east was taken by the Medes and the south was taken by the Neo-Babylonians. Assyria's hegemony was reduced to just its core area until even that was defeated in 612 BC. There were a few more destructions before Nineveh was totally obliterated. Perhaps foreseeing this end, Ashurbanipal gathered works from far and wide and formed a library that provides much of our knowledge of the region's culture.