You mean specifically explorers? Probably any of the explorers that were on land and travelling had to be very careful about how they interacted with the Indians. Without a fort or some defensive works, they were outnumbered and on the natives home turf, so I suspect they treated the native very well. But once the land speculators came in and their were forts for protection, anything could happen. Check out Lewis and Clarks exploration of the north west. I believe Sacajawea was instrumental in helping communicate with several tribes that Lewis and Clark were friendly. He wasn't an explorer, but William Penn and the Quakers were very respectful of the Indians. I believe I read somewhere in England in the late 1700s when the anti-slavery groups were forming there was also one for the 'protection of indigenous peoples' or something, but I couldn't find anything with google. I believe the Spanish missions were trying to convert Indians but also protected them from Spanish settlers.