The Spanish Dominican Antón de Montesinos (ca. 1480–1540) worked as a missionary in the region of today's Dominican Republic and Haiti. He was one of the first Europeans to criticize slavery. Not only did he oppose the local settlers, but he also initiated important reforms.
Monumento Fray Antón de Montesinos, 2019, photograph: Mariordo; source: Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Monumento_Fray_Antonio_de_Montesinos_SD_08_2019_7873.jpg, Attribution-ShareAlike 4.0 International (CC BY-SA 4.0), https://creativecommons.org/licenses/by-sa/4.0/deed.en.