Genesis 10:8-10 mentions a "Nimrod" as a founder of cities in Shinar (Sumeria) and Assyria, who is also called a "Mighty Hunter Before the Lord." Yesterday, reading a classical historical work on the history of "Chaldea" by George Rawlinson, a set of story ideas about Nimrod crossed my mind.
Rawlinson mentioned he believed the early Mesopotamians had worshipped Nimrod after his death and that as a god, his worship supplanted that of the original creator god, called Il in Akkadian, which is like the El or Elohim of Hebrew, the God of the Bible. I thought, "What if Nimrod, a heroic figure no doubt, had set himself up to be worshipped during his lifetime, like the Roman emperors?" So perhaps some of his friends and companions also became worshipped as gods, creating the first truly polytheistic system. I'm of course taking the Biblical point of view that all humans once knew the one creator God--so polytheism would have to be a later invention--something this story would explain the origin of from a semi-Biblical viewpoint.
Such a story handled in the simplest and most straightforward way would be historical fiction. Nimrod would be portrayed as a genius conqueror and civilizer, a sort of Napoleon + Ghengis Khan + Julius Caesar, who carries sinister megalomaniac tendencies that manifest them in outright wicked self-worship in the end. Perhaps a coalition of ancient good guys defeat Nimrod in Shinar, causing him to flee north to begin his work all over again in Assyria.
Since, though, Nimrod defies the one true God in the story, a view of the spiritual world could be brought into the tale, which would make a form of supernatural speculative fiction, angels and demons manifesting themselves in the tale as heaven and hell join in the ancient struggle.
Playing up some of the supernatural aspects to the point where Nimrod or his associates master the use of magic and create magical weapons and whatnot, would make the story a form of fantasy.
Having Nimrod direct the building of the Tower of Babel for the purpose of contacting ancient aliens of some sort would be off-track of what I'd want to write, but would definitely pull the story into the realm of science fiction, especially if the aliens are portrayed in some way (please bear in mind aliens can be portrayed even in a work from a deliberately Biblical viewpoint, but the aliens must somehow be shown to be creations of God).
Lastly, this story could be written up from the point of Biblical history. What scant Biblical evidence of Nimrod that exists could be discussed, parallels drawn between him and other human rulers diametrically opposed to God, such as Antiochus Epiphanes, the pharaoh of Exodus, Titus (who destroyed Jerusalem), and the coming Antichrist, among others. Or perhaps it would be better to write about the historical series of antichrists, making Nimrod a "probable" first one.
So if I only had an extra ten years or so on my hands, I could write all of them...