The answer becomes clear if we do a little bit of editing to the title and say that Jesus is “King of kings, and Lord of lords.” By lowercasing both “kings” and “lords” we can see that the kings and lords referred to are human and angelic monarchs and nobles—nobles often being referred to by the courtesy title of “lord” in English. In other words, Christ is ruler over all creation, including over all creatures who are themselves rulers of some sort.