It was an act of domination and condescension for American slaveowners to name their slaves after "great" men of antiquity, given that the slaves had no means of knowing who their namesakes were (or what a word like "emperor" meant). It was strictly for their own amusement, and because they read Latin and Greek and liked to have references to the Classics around themselves. So we get names of specific people or figures, like Venus, Apollo, Hercules, or Bacchus; Cicero, Cato, Augustus, Scipio, or Pompey; and generic ancient terms like emperor.

There is a similar phenomenon with biblical names, though the impetus for this was less condescension and mockery and more a goal of "teaching" and Christianizing. The general pattern is the same, though, with slave names like Moses and Abraham.

Slave families of course named their offspring themselves, even if it was supplanted by owner-given names. They often named children based on the happenings of the birth day, like weather, geography, or the day of the week

For a concise discussion of this, see Kolchin, American Slavery: 1619-1877