For a man who is considered the founder of two of the greatest cities of the ancient world: Babylon and Nineveh, Nimrod hardly appears in the Bible. Even so, the picture of the man, a descendent of Ham, son of Noah, appears formidable.
Cush was the father of Nimrod, who grew to be a mighty warrior on the earth. He was a mighty hunter before the LORD ; that is why it is said, "Like Nimrod, a mighty hunter before the LORD." The first centers of his kingdom were Babylon, Erech, Akkad and Calneh, in Shinar. From that land he went to Assyria, where he built Nineveh, Rehoboth Ir, Calah 12 and Resen, which is between Nineveh and Calah; that is the great city.
Nimrod was not just a powerful man on the earth at that time, he was a tyrannical leader of men. The phrase "a mighty hunter before the Lord" suggests that it was not wild beasts that Nimrod was hunting, but men. Having hunted them he would enslave them and have a tyranical hold over them. And all this was done in direct opposition to the Lord.
It has also been suggested that Nimrod tamed a leopard to accompany him on his hunts for animals, just as people today use dogs for this purpose. This could also be where Nimrod got his name: the Babylonian name for "leopard" was "nimr" and "rod" means "to subdue."
After the Great Flood, various city-states in Mesopotamia became the temporary seat of power until about 2800 BC, when they were united under the rule of one king, Etana of Kish, who may also be the origin of the Biblical Nimrod. Seven cities were conquered by this king, who established the world's first, post-deluge empire. After founding a southern (Sumerian) empire in Babel, Erech, Akkad, and Calneh, he invaded Assyria and built Nineveh, Rehoboth-Ir, Calah and Resen. He then unified the people in numerous construction projects, the most prominent of which was the construction of the Tower of Babel. (source: The Rise and Fall of Nimrod)