Who was a spanish missionary who spoke out against the mistreatment of native America?

The Spanish missionary who spoke out most forcefully against the mistreatment of Native Americans was Bartolomé de las Casas.

He was a Dominican friar who:

* Wrote extensively about the atrocities committed against indigenous peoples in the Americas, including the brutal exploitation of their labor, forced conversions, and mass killings.

* Argued for their humanity and their right to be treated with respect and dignity.

* Advocated for their protection and opposed the encomienda system, which granted Spanish colonists control over Native American labor.

Although his efforts were met with resistance from many powerful figures in Spain and the Americas, his writings and activism are considered crucial in raising awareness about the injustices faced by Native Americans.