Gen. 10:8 And Cush begat Nimrod: he began to be a mighty one in the earth. 9 He was a mighty hunter before the LORD: wherefore it is said, Even as Nimrod the mighty hunter before the LORD. 10 And the beginning of his kingdom was Babel, and Erech, and Accad, and Calneh, in the land of Shinar.
It looks like Nimrod was a type of Cain. Instead of ruling the land he ruled the animal kingdom. As a hunter he would have access to many animals, but I don't see him ever offering one of them to the Lord in sacrifice. You wold think that he had learned some thing from the stories passed down through Noah about the time before the flood.