Who was the first person to oppose slave trading?

550 BC: Slavery in Achaemenid Persia was generally banned. Zoroastrianism, the religion of the empire, explicitly forbids slavery and the kings of Achaemenid Persia, especially the founder Cyrus the Great, followed this ban to varying degrees. This was evidenced by the freeing of the Jews at Babylon, and the construction of Persepolis by paid workers.